Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Jul. 26, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Entity File Number	001-37806
Entity Registrant Name	TWILIO INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-2574840
Entity Address, Address Line One	375 Beale Street
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94105
City Area Code	415
Local Phone Number	390-2337
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Class A Common Stock, par value $0.001 per share
Trading Symbol	TWLO
Security Exchange Name	NYSE
Entity Central Index Key	0001447669
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Common Class A
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		121,541,496
Common Class B
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		14,346,097

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 535,911	$ 487,215
Short-term marketable securities	1,346,371	261,128
Accounts receivable, net	126,780	97,712
Prepaid expenses and other current assets	50,451	26,893
Total current assets	2,059,513	872,948
Restricted cash	862	18,119
Property and equipment, net	106,480	63,534
Operating right of use asset	151,946	0
Intangible assets, net	485,410	27,558
Goodwill	2,283,578	38,165
Other long-term assets	21,316	8,386
Total assets	5,109,105	1,028,710
Current liabilities:
Accounts payable	29,361	18,495
Accrued expenses and other current liabilities	117,625	96,343
Deferred revenue and customer deposits	24,898	22,972
Operating lease liability, current	21,858	0
Financing lease liability, current	5,920	0
Note payable, current	2,119	0
Total current liabilities	201,781	137,810
Operating lease liability, noncurrent	138,819	0
Financing lease liability, noncurrent	7,752	0
Note payable, noncurrent	2,237	0
Convertible senior notes, net	446,177	434,496
Other long-term liabilities	15,479	18,169
Total liabilities	812,245	590,475
Commitments and contingencies (Note 12)
Stockholders’ equity:
Preferred stock	0	0
Class A and Class B common stock	136	100
Additional paid-in capital	4,794,177	808,527
Accumulated other comprehensive income	3,303	1,282
Accumulated deficit	(500,756)	(371,674)
Total stockholders’ equity	4,296,860	438,235
Total liabilities and stockholders’ equity	$ 5,109,105	$ 1,028,710

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Revenue	$ 275,039	$ 147,754	$ 508,178	$ 276,870
Cost of revenue	125,024	67,940	232,113	127,522
Gross profit	150,015	79,814	276,065	149,348
Operating expenses:
Research and development	98,783	39,811	176,638	77,387
Sales and marketing	90,421	37,749	162,028	70,571
General and administrative	54,543	24,212	118,719	47,605
Total operating expenses	243,747	101,772	457,385	195,563
Loss from operations	(93,732)	(21,958)	(181,320)	(46,215)
Other expenses, net	(880)	(1,898)	(1,516)	(1,233)
Loss before provision for income taxes	(94,612)	(23,856)	(182,836)	(47,448)
Income tax benefit (provision)	2,033	(150)	53,754	(287)
Net loss attributable to common stockholders	$ (92,579)	$ (24,006)	$ (129,082)	$ (47,735)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.72)	$ (0.25)	$ (1.05)	$ (0.50)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	129,310,641	96,348,356	122,985,716	95,515,583

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (92,579)	$ (24,006)	$ (129,082)	$ (47,735)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	980	152	2,021	(165)
Foreign currency translation	0	(629)	0	102
Total other comprehensive income (loss)	980	(477)	2,021	(63)
Comprehensive loss attributable to common stockholders	$ (91,599)	$ (24,483)	$ (127,061)	$ (47,798)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (129,082)	$ (47,735)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	49,610	11,392
Right-of-use asset amortization	10,707	0
Net amortization of investment premium and discount	(2,948)	(237)
Amortization of debt discount and issuance costs	11,682	2,695
Stock-based compensation	129,064	38,546
Amortization of deferred commissions	1,585	478
Provision for doubtful accounts	697	1,515
Tax benefit related to release of valuation allowance	(53,502)	0
Write-off of long lived assets	769	515
Other tax benefit realized in the period	(692)	0
Changes in operating assets and liabilities:
Accounts receivable	(22,523)	(26,048)
Prepaid expenses and other current assets	(15,688)	(2,847)
Other long-term assets	(5,969)	(1,908)
Accounts payable	8,306	12,566
Accrued expenses and other current liabilities	13,976	28,040
Deferred revenue and customer deposits	1,927	3,300
Operating right of use liability	(9,367)	0
Long-term liabilities	(2,371)	(1,047)
Net cash (used in) provided by operating activities	(13,819)	19,225
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisitions, net of cash acquired	146,957	0
Purchases of marketable securities and other investments	(1,377,072)	(184,364)
Proceeds from sales and maturities of marketable securities	286,653	58,520
Capitalized software development costs	(10,520)	(9,958)
Purchases of long-lived assets	(7,882)	(2,315)
Net cash used in investing activities	(961,864)	(138,117)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from a public offering, net of underwriting discount	980,000	0
Payments of costs related to the public offering	(347)	0
Proceeds from issuance of convertible senior notes	0	550,000
Payment of debt issuance costs	0	(12,513)
Purchase of capped call	0	(58,465)
Principal payments on notes payable	(997)	0
Principal payments on financing leases	(2,463)	0
Proceeds from exercises of stock options	25,255	13,715
Proceeds from shares issued under ESPP	8,254	4,474
Value of equity awards withheld for tax liabilities	(2,580)	(910)
Net cash provided by financing activities	1,007,122	496,301
Effect of exchange rate changes on cash, cash equivalents and restricted cash	0	818
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	31,439	378,227
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—Beginning of period	505,334	120,788
CASH, CASH EQUIVALENTS AND RESTRICTED CASH —End of period	536,773	499,015
Cash paid for income taxes, net	48	321
Cash paid on finance leases	337	0
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property, equipment and intangible assets, accrued but not paid	1,831	572
Purchases of property and equipment through finance leases	13,616	0
Acquisition holdback	4,230
Acquisition - value of common stock issued, stock awards assumed and measurement period adjustments	2,843,392	0
Stock-based compensation capitalized in software development costs	3,244	2,909
Debt offering costs, accrued but not paid	0	467
Costs related to public offerings, accrued but not paid	$ 606	$ 0

Condensed Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock Common Class A	Common Stock Common Class B	Additional Paid In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Follow-on Public Offering Common Class A
Balance (in shares) at Dec. 31, 2017		69,906,550	24,063,246
Balance at Dec. 31, 2017	$ 359,846	$ 70	$ 24	$ 608,165	$ 2,025	$ (250,438)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(23,729)					(23,729)
Adjustment to opening retained earnings due to adoption of ASC 606	713					713
Exercise of vested stock options (in shares)			1,190,387
Exercise of vested stock options	6,678		$ 1	6,677
Vesting of early exercised stock options	21			21
Vesting of restricted stock units (in shares)		491,501	52,716
Value of equity awards withheld for tax liability (in shares)		(8,352)	(4,380)
Value of equity awards withheld for tax liability	(371)			(371)
Conversion of shares of Class B common stock into shares of Class A common stock (in shares)		1,358,716	(1,358,716)
Conversion of shares of Class B common stock into shares of Class A common stock		$ 1	$ (1)
Unrealized gain (loss) on marketable securities	(317)				(317)
Foreign currency translation	731				731
Stock-based compensation	18,968			18,968
Balance (in shares) at Mar. 31, 2018		71,748,415	23,943,253
Balance at Mar. 31, 2018	362,540	$ 71	$ 24	633,460	2,439	(273,454)
Balance (in shares) at Dec. 31, 2017		69,906,550	24,063,246
Balance at Dec. 31, 2017	359,846	$ 70	$ 24	608,165	2,025	(250,438)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on marketable securities	(165)
Foreign currency translation	102
Balance (in shares) at Jun. 30, 2018		76,511,357	20,828,123
Balance at Jun. 30, 2018	429,671	$ 75	$ 21	725,073	1,962	(297,460)
Balance (in shares) at Dec. 31, 2017		69,906,550	24,063,246
Balance at Dec. 31, 2017	359,846	$ 70	$ 24	608,165	2,025	(250,438)
Balance (in shares) at Dec. 31, 2018		80,769,763	19,310,465
Balance at Dec. 31, 2018	438,235	$ 80	$ 20	808,527	1,282	(371,674)
Balance (in shares) at Mar. 31, 2018		71,748,415	23,943,253
Balance at Mar. 31, 2018	362,540	$ 71	$ 24	633,460	2,439	(273,454)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(24,006)					(24,006)
Exercise of vested stock options (in shares)			960,414
Exercise of vested stock options	7,037		$ 1	7,036
Vesting of early exercised stock options	4			4
Vesting of restricted stock units (in shares)		457,495	40,070
Value of equity awards withheld for tax liability (in shares)		(5,860)	(5,888)
Value of equity awards withheld for tax liability	(539)			(539)
Conversion of shares of Class B common stock into shares of Class A common stock (in shares)		4,109,726	(4,109,726)
Conversion of shares of Class B common stock into shares of Class A common stock		$ 4	$ (4)
Unrealized gain (loss) on marketable securities	152				152
Foreign currency translation	(629)				(629)
Shares issued under ESPP (in shares)		201,581
Shares issued under ESPP	4,474			4,474
Issuance of debt conversion option	119,435			119,435
Debt conversion option issuance costs	(2,819)			(2,819)
Capped call option issuance costs	(58,465)			(58,465)
Stock-based compensation	22,487			22,487
Balance (in shares) at Jun. 30, 2018		76,511,357	20,828,123
Balance at Jun. 30, 2018	429,671	$ 75	$ 21	725,073	1,962	(297,460)
Balance (in shares) at Dec. 31, 2018		80,769,763	19,310,465
Balance at Dec. 31, 2018	438,235	$ 80	$ 20	808,527	1,282	(371,674)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(36,503)					(36,503)
Exercise of vested stock options (in shares)		748,679	1,023,984
Exercise of vested stock options	15,328	$ 1	$ 1	15,326
Vesting of early exercised stock options	9			9
Vesting of restricted stock units (in shares)		641,406	39,360
Value of equity awards withheld for tax liability (in shares)		(5,860)	(4,431)
Value of equity awards withheld for tax liability	(1,062)			(1,062)
Conversion of shares of Class B common stock into shares of Class A common stock (in shares)		4,339,519	(4,339,519)
Conversion of shares of Class B common stock into shares of Class A common stock		$ 4	$ (4)
Shares issued in acquisition (in shares)		23,555,081
Shares issued in acquisition	2,658,898	$ 24		2,658,874
Unrealized gain (loss) on marketable securities	1,041				1,041
Equity awards assumed in acquisition	191,620			191,620
Stock-based compensation	59,947			59,947
Balance (in shares) at Mar. 31, 2019		110,048,588	16,029,859
Balance at Mar. 31, 2019	3,327,513	$ 109	$ 17	3,733,241	2,323	(408,177)
Balance (in shares) at Dec. 31, 2018		80,769,763	19,310,465
Balance at Dec. 31, 2018	438,235	$ 80	$ 20	808,527	1,282	(371,674)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on marketable securities	2,021
Foreign currency translation	0
Balance (in shares) at Jun. 30, 2019		121,377,614	14,384,746
Balance at Jun. 30, 2019	4,296,860	$ 120	$ 16	4,794,177	3,303	(500,756)
Balance (in shares) at Mar. 31, 2019		110,048,588	16,029,859
Balance at Mar. 31, 2019	3,327,513	$ 109	$ 17	3,733,241	2,323	(408,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(92,579)					(92,579)
Exercise of vested stock options (in shares)		313,924	503,797
Exercise of vested stock options	9,927		$ 1	9,926
Vesting of restricted stock units (in shares)		675,028	29,576
Vesting of restricted stock units	1	$ 1
Value of equity awards withheld for tax liability (in shares)		(5,934)	(5,888)
Value of equity awards withheld for tax liability	(1,518)			(1,518)
Conversion of shares of Class B common stock into shares of Class A common stock (in shares)		2,172,598	(2,172,598)
Conversion of shares of Class B common stock into shares of Class A common stock		$ 2	$ (2)
Shares issued in acquisition (in shares)							8,064,515
Shares issued in acquisition	980,000	$ 8		979,992
Unrealized gain (loss) on marketable securities	980				980
Foreign currency translation	0
Shares issued under ESPP (in shares)		108,895
Shares issued under ESPP	8,254			8,254
Costs related to public offering	(953)			(953)
Equity awards assumed in acquisition	(7,126)			(7,126)
Stock-based compensation	72,361			72,361
Balance (in shares) at Jun. 30, 2019		121,377,614	14,384,746
Balance at Jun. 30, 2019	$ 4,296,860	$ 120	$ 16	$ 4,794,177	$ 3,303	$ (500,756)

Organization and Description of Business	6 Months Ended
Organization and Description of Business	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Twilio Inc. (the “Company”) was incorporated in the state of Delaware on March 13, 2008. The Company is the leader in the Cloud Communications Platform category and enables developers to build, scale and operate real-time communications within their software applications via simple-to-use Application Programming Interfaces (“API”). The power, flexibility, and reliability offered by the Company’s software building blocks empower entities of virtually every shape and size to build world-class engagement into their customer experience. The Company’s headquarters are located in San Francisco, California, and the Company has subsidiaries in Australia, Bermuda, Colombia, Czech Republic, Estonia, France, Germany, Hong Kong, Ireland, Japan, the Netherlands, Singapore, Spain, Sweden, United Kingdom and the United States.

Summary of Significant Accounting Policies	6 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies (a)Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in our Annual Report on Form 10-K filed with the SEC on March 1, 2019 (“Annual Report”). The condensed consolidated balance sheet as of December 31, 2018, included herein, was derived from the audited financial statements as of that date, but may not include all disclosures including certain notes required by U.S. GAAP on an annual reporting basis. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the financial position, results of operations, comprehensive loss and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2019 or any future period. (b)Principles of Consolidation The condensed consolidated financial statements include the Company and its wholly owned subsidiaries. All significant intercompany balances and transactions have been eliminated. (c)Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are used for, but not limited to, revenue allowances and returns; recoverability of long-lived and intangible assets; capitalization and useful life of the Company’s capitalized internal-use software development costs; fair value of acquired intangible assets and goodwill; accruals and contingencies. Estimates are based on historical experience and on various assumptions that the Company believes are reasonable under current circumstances. However, future events are subject to change and best estimates and judgments may require further adjustments; therefore, actual results could differ materially from those estimates. Management periodically evaluates such estimates and they are adjusted prospectively based upon such periodic evaluation. (d)Concentration of Credit Risk Financial instruments that potentially expose the Company to a concentration of credit risk consist primarily of cash, cash equivalents, marketable securities, restricted cash and accounts receivable. The Company maintains cash, cash equivalents, marketable securities and restricted cash with financial institutions that management believes are financially sound and have minimal credit risk exposure although the balances will exceed insured limits. The Company sells its services to a wide variety of customers. If the financial condition or results of operations of any significant customers deteriorate substantially, operating results could be adversely affected. To reduce credit risk, management performs ongoing credit evaluations of the financial condition of significant customers. The Company does not require collateral from its credit customers and maintains reserves for estimated credit losses on customer accounts when considered necessary. Actual credit losses may differ from the Company’s estimates. During the three and six months ended June 30, 2019 and 2018, respectively, there was no customer organization that accounted for more than 10% of the Company’s total revenue. As of June 30, 2019, and December 31, 2018, no customer organization represented more than 10% of the Company’s gross accounts receivable. (e)Deferred Revenue and Customer Deposits Deferred revenue is recorded when cash payments are received in advance of future usage on non-cancelable contracts. Customer refundable prepayments are recorded as customer deposits. During the three and six months ended June 30, 2019, the Company recognized $4.7 million and $15.4 million of revenue, respectively, and during the three and six months ended June 30, 2018, the Company recognized $3.6 million and $7.2 million of revenue, respectively, that was included in the deferred revenue and customer deposits balance as of the beginning of the year. (f)Deferred Sales Commissions The Company records an asset for the incremental costs of obtaining a contract with a customer, for example, sales commissions that are earned upon execution of contracts. The Company uses the portfolio of data method to determine the estimated period of benefit of capitalized commissions which is determined to be five years. Amortization expense related to these capitalized costs related to initial contracts, upsells and renewals, is recognized on a straight line basis over the estimated period of benefit of the capitalized commissions. Total net capitalized costs as of June 30, 2019, and December 31, 2018, were $17.5 million and $9.4 million, respectively, and are included in prepaid expenses and other current and long‑term assets in the accompanying condensed consolidated balance sheets. Amortization of these assets was $0.9 million and $1.6 million in the three and six months ended June 30, 2019, respectively, and $0.3 million and $0.5 million in the three and six months ended June 30, 2018, respectively, and is included in sales and marketing expense in the accompanying condensed consolidated statements of operations. (g) Recently Adopted Accounting Guidance In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-02, "Leases (Topic 842)", which was further clarified in July 2018 by ASU 2018‑10, “Codification Improvements to Topic 842, Leases”, and ASU 2018‑11, “Leases-Targeted Improvements”. ASU 2018-10 provides narrow amendments to clarify how to apply certain aspects of the new lease standard. ASU 2018-11 addresses implementation issues related to the new lease standard. The standard is effective for interim and annual reporting periods beginning after December 15, 2018. Under the new standard, lessees are required to recognize in the balance sheet the right-of-use ("ROU") assets and lease liabilities that arise from operating leases. The Company adopted the standard using the optional alternative method on a prospective basis with an effective date as of the beginning of the Company’s fiscal year, January 1, 2019, and applied it to the operating leases that existed on that date. Prior year comparative financial information was not recast under the new standard and continues to be presented under ASC 840. The Company elected to utilize the package of practical expedients available for expired or existing contracts which allowed the Company to carryforward historical assessments of (a) whether contracts are or contain leases, (b) lease classification, and (c) initial direct costs. The Company elected the use of hindsight practical expedient in determining the lease term and assessing the likelihood that lease renewal, termination or purchase option will be exercised. The Company also elected to apply the short-term lease exception for all leases. Under the short-term lease exception, the Company will not recognize ROU assets or lease liabilities for leases that, at the acquisition date, have a remaining lease term of 12 months or less. As a result of implementing this guidance, the Company recognized a $123.5 million net operating ROU asset and a $132.0 million operating lease liability in its condensed consolidated balance sheet as of January 1, 2019. The ROU asset was presented net of deferred rent of $9.0 million as of January 1, 2019, in the accompanying condensed consolidated balance sheet and as a change within operating cash flows. In addition, on February 1, 2019, the Company acquired through its business combination with SendGrid approximately $33.7 million in operating ROU assets, $32.6 million in operating lease liability, $14.2 million in finance ROU assets and $13.6 million in finance lease liability. The Company measured the lease liability at the present value of the future lease payments as of January 1, 2019. The Company used its incremental borrowing rate to discount the lease payments. The Company derived the discount rate, adjusted for differences in the term and payment patterns, from the information available at the adoption date. The right-of-use asset is valued at the amount of the lease liability adjusted for the remaining December 31, 2018, balance of unamortized lease incentives, prepaid rent and deferred rent. The lease liability is subsequently measured at the present value of unpaid future lease payments as of the reporting date with a corresponding adjustment to the right-of-use asset. Absent a lease modification, the Company will continue to utilize the January 1, 2019, incremental borrowing rate. The Company recognizes lease costs on a straight-line basis and presents these costs as operating expenses within the consolidated statements of operations and comprehensive loss. The Company presents lease payments within the cash flows from operations within the consolidated statements of cash flows. The financial results for the three and six months ended June 30, 2019, are presented under the new standard, while the comparative periods presented are not adjusted and continue to be reported in accordance with the Company’s historical accounting policy. See Note 5, “Right-of-use Assets and Lease Liabilities” for further information. In March 2019, the FASB issued ASU 2019-01, “Codification Improvements” to Leases (Topic 842). This pronouncement did not have a material impact on the Company's financial statements. In August 2018, the FASB issued ASU 2018‑13, “Fair Value Measurement (Topic 820) Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement”. The amendments under ASU 2018‑13 remove, add and modify certain disclosure requirements on fair value measurements in ASC 820. The amendments are effective for interim and annual periods beginning after December 15, 2019. The Company early adopted this guidance effective April 1, 2019. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. In July 2018, the FASB issued ASU 2018-09, "Codification Improvements ", which does not prescribe any new accounting guidance, but instead makes minor improvements and clarifications of several topics. Certain updates are applicable immediately while others provide for a transition period to adopt as part of the next fiscal year beginning after December 15, 2018. The Company adopted this guidance effective April 1, 2019. The adoptions of this guidance did not have a material impact on the Company's consolidated financial statements. In January 2017, the FASB issued ASU 2017‑04, “Simplifying the Test for Goodwill Impairment”, which removes the second step of the goodwill impairment test that requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. This guidance is effective prospectively for interim and annual reporting periods beginning after December 15, 2019. The Company early adopted this guidance effective April 1, 2019. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. (h) Recently Issued Accounting Guidance, Not yet Adopted In August 2018, the FASB issued ASU 2018‑15, “Intangibles—Goodwill and Other—Internal‑Use Software (Subtopic 350‑40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract”. This standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal‑use software. The standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In June 2016, the FASB issued ASU 2016‑13, “Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments”, which changes the impairment model for most financial assets. The new model uses a forward‑looking expected loss method, which will generally result in earlier recognition of allowances for losses. In November 2018, the FASB issued ASU 2018‑19, “Codification Improvements to Topic 326, Financial Instruments—Credit Losses”, which clarifies that receivables arising from operating leases are not within the scope of Topic 326, Financial Instruments—Credit Losses. Instead, impairment of receivables arising from operating leases should be accounted for in accordance with Topic 842, Leases. In April 2019, the FASB issued ASU 2019-04, "Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments," which clarifies treatment of certain credit losses. In May 2019, the FASB issued ASU 2019-05, "Financial Instruments — Credit Losses (Topic 326): Targeted Transition Relief", which permits an entity, upon adoption of ASU 2016-13, to irrevocably elect the fair value option (on an instrument-by-instrument basis) for eligible financial assets measured at amortized cost basis. These ASUs are effective for annual and interim periods beginning after December 15, 2019, and early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements

Fair Value Measurements

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following tables provide the financial assets measured at fair value on a recurring basis as of June 30, 2019, and December 31, 2018, (in thousands):



	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Fair Value Hierarchy as of June 30, 2019						Aggregate Fair Value
	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Level 1		Level 2		Level 3		Aggregate Fair Value
Financial Assets:
Cash and cash equivalents:
Money market funds	$	275,838	$	—	$	—		$	—		$	275,838	$	—	$	—	$	275,838
Reverse repurchase agreements	75,000		—		—			—			—		75,000		—		75,000
Commercial paper	114,471		—		—			—					114,471				114,471
Total included in cash and cash equivalents	465,309		—		—			—			275,838		189,471		—		465,309
Marketable securities:
U.S. Treasury securities	160,374		238		(1		)	—			160,611		—		—		160,611
Corporate debt securities and commercial paper	1,183,653		2,427		(309		)	(11		)	5,000		1,180,760		—		1,185,760
Total marketable securities	1,344,027		2,665		(310		)	(11		)	165,611		1,180,760		—		1,346,371
Strategic investment	5,000		—		—			—			—		—		5,000		5,000
Total financial assets	$	1,814,336	$	2,665	$	(310	)	$	(11	)	$	441,449	$	1,370,231	$	5,000	$	1,816,680



	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Fair Value Hierarchy as of December 31, 2018						Aggregate Fair Value
	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Level 1		Level 2		Level 3		Aggregate Fair Value
Financial Assets:
Cash and cash equivalents:
Money market funds	$	420,234	$	—	$	—		$	—		$	420,234	$	—	$	—	$	420,234
Reverse repurchase agreements	35,000		—		—			—			—		35,000		—		35,000
Commercial paper	9,983		—		—			—			—		9,983		—		9,983
Total included in cash and cash equivalents	465,217		—		—			—			420,234		44,983		—		465,217
Marketable securities:
U.S. Treasury securities	59,785		—		(7		)	(9		)	59,769		—		—		59,769
Corporate debt securities and commercial paper	201,683		23		(123		)	(224		)	—		201,359		—		201,359
Total marketable securities	261,468		23		(130		)	(233		)	59,769		201,359		—		261,128
Total financial assets	$	726,685	$	23	$	(130	)	$	(233	)	$	480,003	$	246,342	$	—	$	726,345

As the Company views its marketable securities as available to support current operations, it has classified all available for sale securities as short-term. As of June 30, 2019, and December 31, 2018, for fixed income securities that were in unrealized loss positions, the Company has determined that (i) it does not have the intent to sell any of these investments, and (ii) it is not more likely than not that it will be required to sell any of these investments before recovery of the entire amortized cost basis. In addition, as of June 30, 2019, and December 31, 2018, the Company anticipates that it will recover the entire amortized cost basis of such fixed income securities and has determined that no other-than-temporary impairments associated with credit losses were required to be recognized during the three and six months ended June 30, 2019 and 2018.

Interest earned on marketable securities was $2.6 million and $4.1 million in the three and six months ended June 30, 2019, respectively, and $0.7 million and $1.4 million in the three and six months ended June 30, 2018, respectively. The interest is recorded as other expense, net, in the accompanying condensed consolidated statements of operations.

The following table summarizes the contractual maturities of marketable securities as of June 30, 2019, and December 31, 2018, (in thousands):



	As of June 30, 2019				As of December 31, 2018
	Amortized Cost		Aggregate Fair Value		Amortized Cost		Aggregate Fair Value
Financial Assets:
Less than one year	$	687,642	$	688,388	$	261,468	$	261,128
One to two years	656,385		657,983		—		—
Total	$	1,344,027	$	1,346,371	$	261,468	$	261,128

The Company enters into reverse securities repurchase agreements, primarily for short-term investments with maturities of 90 days or less. As of June 30, 2019, and December 31, 2018, the Company was party to reverse repurchase agreements totaling $75.0 million and $35.0 million, respectively, which were reported in cash and equivalents in the accompanying condensed consolidated balance sheets. Under these reverse securities repurchase agreements, the Company typically lends available cash at a specified rate of interest and holds U.S. government securities as collateral during the term of the agreement. Collateral value is in excess of the amounts loaned under these agreements.

In May 2019, the Company made a strategic investment of $5.0 million into a privately held debt security in which the Company does not have a controlling interest or significant influence. The security and the bifurcated embedded derivatives are recorded at fair value in other long-term assets in the accompanying condensed consolidated balance sheet. Changes in fair value of the host contract will be recorded in the accumulated other comprehensive income in the Company's consolidated balance sheet, and changes in fair value of the bifurcated derivatives will be recorded in the consolidated statement of operations. The Company classifies its privately held debt security as a Level 3 investment within the fair value hierarchy based on the nature of the fair value inputs. No impairment was recognized for the three months ended June 30, 2019.

As of June 30, 2019, and December 31, 2018, the fair value of the 0.25% convertible senior notes due 2023 (the “Notes”), as further described in Note 9 below, was approximately $1,116.2 million and $743.4 million, respectively. The fair value of the Notes is determined based on the closing price on the last trading day of the reporting period and is classified as a Level 2 security within the fair value hierarchy.

As of June 30, 2019, the note payable assumed in the SendGrid acquisition, as further described in Note 9 below, is recorded at its carrying amount, which approximates its fair value based on the proximity of its effective interest rate to the current market rates. The note payable is classified as a Level 2 instrument within the fair value hierarchy.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment

6 Months Ended

Jun. 30, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consisted of the following (in thousands):



	As of June 30, 2019			As of December 31, 2018
Capitalized internal-use software development costs	$	85,145		$	72,647
Data center equipment ⁽¹⁾	14,795			—
Leasehold improvements	33,305			15,293
Office equipment	20,715			13,563
Furniture and fixtures ⁽¹⁾	7,273			4,918
Software	6,073			1,849
Total property and equipment	167,306			108,270
Less: accumulated depreciation and amortization	(60,826		)	(44,736		)
Total property and equipment, net	$	106,480		$	63,534

_______________


⁽¹⁾	Data center equipment and furniture and fixtures contain assets under finance leases. See Note 5 for further detail.

Depreciation and amortization expense was $9.1 million and $16.7 million for the three and six months ended June 30, 2019, respectively, and $4.3 million and $8.5 million for the three and six months ended June 30, 2018, respectively.

The Company capitalized $6.7 million and $13.7 million in internal-use software development costs in the three and six months ended June 30, 2019, respectively, and $6.7 million and $13.1 million in the three and six months ended June 30, 2018, respectively. Of this amount, stock-based compensation expense was $1.6 million and $3.2 million in the three and six months ended June 30, 2019, respectively, and $1.5 million and $2.9 million in the three and six months ended June 30, 2018, respectively.

Amortization of capitalized software development costs was $4.3 million and $8.1 million in the three and six months ended June 30, 2019, respectively, and $3.0 million and $5.7 million in the three and six months ended June 30, 2018, respectively.

Right-of-Use Asset and Lease Liabilities

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Right-of-Use Asset and Lease Liabilities

The Company determines if an arrangement is a lease at inception. The Company presents the operating leases in long-term assets and current and long-term liabilities. Finance lease assets are included in property and equipment, net, and

finance lease liabilities are presented in current and long-term liabilities in the accompanying condensed consolidated balance sheet as of June 30, 2019.

Right-of-use ("ROU") assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As the Company’s leases do not generally provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company’s lease agreements may have lease and non-lease components, which the Company generally accounts for as a single lease component. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term, and variable payments are recognized in the period they are incurred. The Company’s lease agreements do not contain any residual value guarantees. Leases with an initial term of 12 months or less are not recorded on the balance sheet.

The Company has entered into various operating lease agreements for data centers and office space, and various financing leases agreements for data center and office equipment and furniture.

As of June 30, 2019, the Company had 19 leased properties, with remaining lease terms of one year to 10 years, some of which include options to extend the leases for up to five years.

The components of lease expense recorded in the condensed consolidated statement of operations were as follows (in thousands):



	Three Months Ended June 30, 2019		Six Months Ended June 30, 2019
Operating lease cost	$	8,273	$	15,446
Finance lease cost:
Amortization of assets	1,526		2,689
Interest on lease liabilities	189		337
Short-term lease cost	1,905		3,340
Variable lease cost	1,080		1,567
Total net lease cost	$	12,973	$	23,379

Supplemental balance sheet information related to leases was as follows (in thousands):



Leases	Classification	As of June 30, 2019
Assets:
Operating lease assets	Operating right-of-use asset (a)	$	151,946
Finance lease assets	Property and equipment, net of accumulated depreciation (b)	12,970
Total leased assets		$	164,916

Liabilities:
Current
Operating	Operating lease liability, current	$	21,858
Finance	Financing lease liability, current	5,920
Noncurrent
Operating	Operating lease liability, noncurrent	138,819
Finance	Finance lease liability, noncurrent	7,752
Total lease liabilities		$	174,349


(a)	Operating lease assets are recorded net of accumulated amortization of $10.8 million as of June 30, 2019.


(b)	Finance lease assets are recorded net of accumulated depreciation of $2.7 million as of June 30, 2019.

Supplemental cash flow and other information related to leases was as follows (in thousands):



	Six Months Ended June 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	12,145
Operating cash flows from finance leases	$	337
Financing cash flows from finance leases	$	2,463

Weighted average remaining lease term (in years):
Operating leases	6.8
Finance leases	3.1

Weighted average discount rate:
Operating leases	5.8		%
Finance leases	5.2		%

Maturities of lease liabilities were as follows (in thousands):



	As of June 30, 2019
	Operating Leases			Finance Leases
2019 (remaining six months)	$	14,523		$	3,278
2020	30,523			6,015
2021	28,791			3,130
2022	28,249			807
2023	27,762			413
Thereafter	68,106			1,316
Total lease payments	197,954			14,959
Less: imputed interest	(37,277		)	(1,287		)
Total lease obligations	160,677			13,672
Less: current obligations	(21,858		)	(5,920		)
Long-term lease obligations	$	138,819		$	7,752

Disclosures related to periods prior to adoption of the New Lease Standard

Rent expense was $2.1 million and $4.2 million in the three and six months ended June 30, 2018, respectively.

As of June 30, 2019, the Company had an additional operating lease obligation of $1.8 million related to a lease that will commence during third quarter 2019 with a lease term of 2.0 years. The Company had additional operating and finance lease obligations of $43.6 million and $0.7 million, respectively, related to a lease that will commence during the second quarter of fiscal year 2020 with a lease term of 6.8 years.

Future minimum lease payment obligations under noncancelable operating and finance leases were as follows (in thousands):



	As of December 31, 2018
	Operating Leases		Finance Leases
2019	$	24,128	$	306
2020	29,527		512
2021	30,898		573
2022	30,492		590
2023	30,122		608
Thereafter	81,316		1,939
Total lease payments	$	226,483	$	4,528

Right-of-Use Asset and Lease Liabilities

The Company determines if an arrangement is a lease at inception. The Company presents the operating leases in long-term assets and current and long-term liabilities. Finance lease assets are included in property and equipment, net, and

finance lease liabilities are presented in current and long-term liabilities in the accompanying condensed consolidated balance sheet as of June 30, 2019.

Right-of-use ("ROU") assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As the Company’s leases do not generally provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company’s lease agreements may have lease and non-lease components, which the Company generally accounts for as a single lease component. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term, and variable payments are recognized in the period they are incurred. The Company’s lease agreements do not contain any residual value guarantees. Leases with an initial term of 12 months or less are not recorded on the balance sheet.

The Company has entered into various operating lease agreements for data centers and office space, and various financing leases agreements for data center and office equipment and furniture.

As of June 30, 2019, the Company had 19 leased properties, with remaining lease terms of one year to 10 years, some of which include options to extend the leases for up to five years.

The components of lease expense recorded in the condensed consolidated statement of operations were as follows (in thousands):



	Three Months Ended June 30, 2019		Six Months Ended June 30, 2019
Operating lease cost	$	8,273	$	15,446
Finance lease cost:
Amortization of assets	1,526		2,689
Interest on lease liabilities	189		337
Short-term lease cost	1,905		3,340
Variable lease cost	1,080		1,567
Total net lease cost	$	12,973	$	23,379

Supplemental balance sheet information related to leases was as follows (in thousands):



Leases	Classification	As of June 30, 2019
Assets:
Operating lease assets	Operating right-of-use asset (a)	$	151,946
Finance lease assets	Property and equipment, net of accumulated depreciation (b)	12,970
Total leased assets		$	164,916

Liabilities:
Current
Operating	Operating lease liability, current	$	21,858
Finance	Financing lease liability, current	5,920
Noncurrent
Operating	Operating lease liability, noncurrent	138,819
Finance	Finance lease liability, noncurrent	7,752
Total lease liabilities		$	174,349


(a)	Operating lease assets are recorded net of accumulated amortization of $10.8 million as of June 30, 2019.


(b)	Finance lease assets are recorded net of accumulated depreciation of $2.7 million as of June 30, 2019.

Supplemental cash flow and other information related to leases was as follows (in thousands):



	Six Months Ended June 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	12,145
Operating cash flows from finance leases	$	337
Financing cash flows from finance leases	$	2,463

Weighted average remaining lease term (in years):
Operating leases	6.8
Finance leases	3.1

Weighted average discount rate:
Operating leases	5.8		%
Finance leases	5.2		%

Maturities of lease liabilities were as follows (in thousands):



	As of June 30, 2019
	Operating Leases			Finance Leases
2019 (remaining six months)	$	14,523		$	3,278
2020	30,523			6,015
2021	28,791			3,130
2022	28,249			807
2023	27,762			413
Thereafter	68,106			1,316
Total lease payments	197,954			14,959
Less: imputed interest	(37,277		)	(1,287		)
Total lease obligations	160,677			13,672
Less: current obligations	(21,858		)	(5,920		)
Long-term lease obligations	$	138,819		$	7,752

Disclosures related to periods prior to adoption of the New Lease Standard

Rent expense was $2.1 million and $4.2 million in the three and six months ended June 30, 2018, respectively.

As of June 30, 2019, the Company had an additional operating lease obligation of $1.8 million related to a lease that will commence during third quarter 2019 with a lease term of 2.0 years. The Company had additional operating and finance lease obligations of $43.6 million and $0.7 million, respectively, related to a lease that will commence during the second quarter of fiscal year 2020 with a lease term of 6.8 years.

Future minimum lease payment obligations under noncancelable operating and finance leases were as follows (in thousands):



	As of December 31, 2018
	Operating Leases		Finance Leases
2019	$	24,128	$	306
2020	29,527		512
2021	30,898		573
2022	30,492		590
2023	30,122		608
Thereafter	81,316		1,939
Total lease payments	$	226,483	$	4,528

Business Combinations

6 Months Ended

Jun. 30, 2019

Business Combinations [Abstract]

Business Combinations

Fiscal 2019 Acquisitions

Capio, Inc.

In June 2019, the Company acquired all outstanding shares of Capio, Inc. ("Capio"), a developer and provider of an automatic speech recognition technology based in Sunnyvale, California, for a total purchase price of $14.4 million, paid in cash, of which $4.0 million was withheld by the Company for a period of 18 months and an additional $0.2 million was withheld for certain tax liabilities to be settled in the near term. These amounts are recorded in the long-term and short-term liabilities, respectively, in the accompanying condensed consolidated balance sheet as of June 30, 2019.

Additionally, the Company granted 43,556 restricted stock units of the Company's Class A common stock to former Capio stockholders that had a value of $5.9 million and are subject to vesting over a period of three years. The Company is recording stock-based compensation expense as the shares vest.

The acquisition was accounted for as a business combination and the total purchase price was allocated to the net tangible and intangible assets and liabilities based on their fair values on the acquisition date and the excess was recorded as goodwill. The acquired entity's results of operations have been included in the consolidated financial statements of the Company from the date of acquisition.

The following table presents the preliminary purchase price allocation recorded in the Company's condensed consolidated balance sheet as of June 30, 2019, (in thousands):



	Total
Net tangible liabilities assumed	$	(542	)
Intangible assets ⁽¹⁾	7,610
Goodwill ⁽²⁾	7,343
Total purchase price	$	14,411

_________________

⁽¹⁾ Identifiable finite-lived intangible assets were comprised of the following (in thousands):

⁽²⁾ The goodwill is primarily attributable to the future cash flows to be realized from the acquired technology. The goodwill is not deductible for U.S. tax purposes.

The Company acquired a net deferred tax liability of $0.8 million in this business combination that is included in the long-term liabilities in the accompanying condensed consolidated balance sheet.

The estimated fair value of the intangible assets acquired was determined by the Company, and the Company considered and relied in part upon a valuation report of a third-party expert. The Company used an income approach to estimate the fair values of the identifiable intangible assets.

The Company incurred costs related to this acquisition of $0.8 million that were expensed as incurred and recorded in general and administrative expenses in the accompanying condensed consolidated statement of operation.

Pro forma results of operations for this acquisition are not presented as the financial impact to the Company's consolidated financial statements is immaterial.

SendGrid, Inc.

In February 2019, the Company acquired all outstanding shares of SendGrid, Inc. ("SendGrid"), the leading email API platform, by issuing 23.6 million shares of its Class A common stock with a total value of $2,658.9 million . The Company also assumed all of the outstanding stock options and restricted stock units of SendGrid as converted into stock options and restricted stock units, respectively, of the Company based on the conversion ratio provided in the Agreement and Plan of Merger and Reorganization, as amended (the "Merger Agreement").

The acquisition added additional products and services to the Company's offerings for its customers. With these additional products, the Company now offers an Email API and Marketing Campaigns product leveraging the Email API. The acquisition has also added new customers, new employees, technology and intellectual property assets.

The acquisition was accounted for as a business combination and the total purchase price was allocated to the net tangible and intangible assets and liabilities based on their fair values on the acquisition date and the excess was recorded as goodwill. The values assigned to the assets acquired and liabilities assumed are based on preliminary estimates of fair value available as of the date of this Quarterly Report on Form 10-Q and may be adjusted during the measurement period of up to 12 months from the date of acquisition as further information becomes available. In the three months ended June 30, 2019, the Company recorded a measurement period adjustment of $7.1 million to reduce its preliminary purchase price related to the value of the pre-combination services reflected in the assumed equity awards, and $7.0 million to reallocate value between the acquired intangible assets and goodwill. Both adjustments were recorded as a result of further refinement of the assumptions used in the process of valuation of these assets.

As of June 30, 2019, the primary areas that are still not finalized due to information that may become available and may result in further changes in the values assigned to various assets and liabilities include purchase consideration and purchase price, including related tax impact, and valuation of tangible and intangible assets.

The adjusted purchase price of $2,843.4 million reflects the $2,658.9 million fair value of 23.6 million shares of the Company's Class A common stock transferred as consideration for all outstanding shares of SendGrid, and the $184.5 million fair value of the pre-combination services of SendGrid employees reflected in the equity awards assumed by the Company on the acquisition date.

The fair value of the 23.6 million shares transferred as consideration was determined on the basis of the closing market price of the Company's Class A common stock on the acquisition date. The fair value of the equity awards was determined (a) for options, by using a Black-Scholes option pricing model with the applicable assumptions as of the acquisition date, and (b) for restricted stock units, by using the closing market price of the Company's Class A common stock on the acquisition date.

The unvested stock awards assumed on the acquisition date will continue to vest as the SendGrid employees provide services in the post acquisition period. The fair value of these awards will be recorded as share-based compensation expense over the respective vesting period of each award.

The purchase price components, as adjusted, are summarized in the following table (in thousands):



	Total
Fair value of Class A common stock transferred	$	2,658,898
Fair value of the pre-combination service through equity awards	184,494
Total purchase price, as adjusted	$	2,843,392

The following table presents the preliminary purchase price allocation, as adjusted, recorded in the Company's condensed consolidated balance sheet as of June 30, 2019 (in thousands). The Company expects to continue to obtain information to assist it in determining the fair values of the net assets acquired on the acquisition date during the measurement period:



	Total
Cash and cash equivalents	$	156,783
Accounts receivable and other current assets	11,636
Property and equipment, net	38,350
Operating right of use asset	33,742
Intangible assets	483,000
Other assets	1,664
Goodwill	2,238,070
Accounts payable and other liabilities	(11,115		)
Operating lease liability	(32,568		)
Financing lease liability	(13,616		)
Note payable	(5,387		)
Deferred tax liability	(57,167		)
Total purchase price	$	2,843,392

The Company acquired a net deferred tax liability of $57.2 million in this business combination that is included in long-term liabilities in the accompanying condensed consolidated balance sheet. This amount was offset by a release of a valuation allowance on deferred tax assets of $48.6 million.

Identifiable intangible assets are comprised of the following (in thousands):



	Total		Estimated life (in years)
Developed technology and software	$	294,000	7
Customer relationships	169,000		7
Trade names	20,000		5
Total intangible assets acquired	$	483,000

Developed technology consists of software products and domain knowledge around email delivery developed by SendGrid, which enables the delivery of email reliably and at scale. Customer relationships consists of contracts with platform users that purchase SendGrid’s products and services that carry distinct value. Trade names represent the Company’s right to the SendGrid trade names and associated design, as it exists as of the acquisition closing date.

The goodwill is primarily attributable to the future cash flows to be realized from the acquired platform technology, acquired intangibles, assembled workforce and operational synergies. Goodwill is not deductible for tax purposes.

The estimated fair value of the intangible assets acquired was determined by the Company, and the Company considered or relied in part upon a valuation report of a third‑party expert. The Company used an income approach to estimate the fair values of the developed technology, an incremental income approach to estimate the value of the customer relationships and a relief from royalty method to estimate the fair value of the trade name.

Net tangible assets were valued at their respective carrying amounts as of the acquisition date, as the Company believes that these amounts approximate their current fair values.

The acquired entity's results of operations were included in the Company's condensed consolidated financial statements from the date of acquisition, February 1, 2019. For the three and six months ended June 30, 2019, SendGrid contributed net operating revenue of $45.9 million and $74.5 million, respectively, which is reflected in the accompanying condensed consolidated statement of operations. Due to the integrated nature of the Company's operations, the Company believes that it is not practicable to separately identify earnings of SendGrid on a stand-alone basis.

During the three and six months ended June 30, 2019, the Company incurred costs related to this acquisition of $0.5 million and $12.9 million, respectively, that were expensed as incurred and recorded in general and administrative expenses in the accompanying condensed consolidated statement of operations.

The following pro forma condensed combined financial information gives effect to the acquisition of SendGrid as if it were consummated on January 1, 2018 (the beginning of the comparable prior reporting period), and includes pro forma adjustments related to the amortization of acquired intangible assets, share-based compensation expense and direct and incremental transaction costs reflected in the historical financial statements. Specifically, the following adjustments were made:

•For the three and six months ended June 30, 2019, the Company's and SendGrid's direct and incremental transaction costs of $0.5 million and $39.9 million, respectively, are excluded from pro forma condensed combined net loss.

•For the three and six months ended June 30, 2018, the Company's direct and incremental transaction costs of $0.5 million and $12.9 million, respectively, are included in the pro forma condensed combined net loss.

•In the three months ended June 30, 2019, the pro forma condensed combined net loss includes an increase to the valuation allowance of $0.6 million. In the six months ended June 30, 2019, the pro forma condensed combined net loss includes a reversal of the valuation allowance release of $48.6 million.

•In the three and six months ended June 30, 2018, the pro forma condensed combined net loss includes a tax expense of $2.6 million and a tax benefit of $53.5 million, respectively, that would have resulted from the acquisition.

This data is presented for informational purposes only and is not intended to represent or be indicative of the results of operations that would have been reported had the acquisition occurred on January 1, 2018. It should not be taken as representative of future results of operations of the combined company.

The following table presents the pro forma condensed combined financial information (in thousands):



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Revenue	$	275,039		$	183,429		$	521,924		$	345,114
Net loss attributable to common stockholders	$	(82,880	)	$	(53,858	)	$	(155,840	)	$	(73,339	)

Goodwill and Intangible Assets

6 Months Ended

Jun. 30, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and intangible assets

Goodwill and Intangible Assets

Goodwill

Goodwill balance as of June 30, 2019, and December 31, 2018, was as follows (in thousands):



	Total
Balance as of December 31, 2018	$	38,165
Goodwill additions related to 2019 acquisitions	2,246,398
Measurement period adjustments	(985		)
Balance as of June 30, 2019	$	2,283,578

Intangible assets

Intangible assets consisted of the following (in thousands):



	As of June 30, 2019
	Gross		Accumulated Amortization			Net
Amortizable intangible assets:
Developed technology	$	328,598	$	(30,581	)	$	298,017
Customer relationships	178,374		(13,280		)	165,094
Supplier relationships	2,696		(1,240		)	1,456
Trade names	20,060		(1,727		)	18,333
Patent	2,439		(224		)	2,215
Total amortizable intangible assets	532,167		(47,052		)	485,115
Non-amortizable intangible assets:
Domain names	32		—			32
Trademarks	263		—			263
Total	$	532,462	$	(47,052	)	$	485,410



	As of December 31, 2018
	Gross		Accumulated Amortization			Net
Amortizable intangible assets:
Developed technology	$	28,209	$	(10,497	)	$	17,712
Customer relationships	8,153		(2,411		)	5,742
Supplier relationships	2,696		(973		)	1,723
Trade name	60		(60		)	—
Patent	2,264		(178		)	2,086
Total amortizable intangible assets	41,382		(14,119		)	27,263
Non-amortizable intangible assets:
Domain names	32		—			32
Trademarks	263		—			263
Total	$	41,677	$	(14,119	)	$	27,558

Amortization expense was $19.3 million and $32.9 million for the three and six months ended June 30, 2019, respectively, and $1.4 million and $2.8 million for the three and six months ended June 30, 2018, respectively.

Total estimated future amortization expense was as follows (in thousands):



	As of June 30, 2019
2019 (remaining six months)	$	39,878
2020	77,882
2021	76,371
2022	74,976
2023	72,786
Thereafter	143,222
Total	$	485,115

Accrued Expenses and Other Liabilities

6 Months Ended

Jun. 30, 2019

Accrued Liabilities and Other Liabilities [Abstract]

Accrued Expenses and Other Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):



	As of June 30, 2019		As of December 31, 2018
Accrued payroll and related	$	15,717	$	9,886
Accrued bonus and commission	8,974		8,564
Accrued cost of revenue	34,523		29,901
Sales and other taxes payable	27,499		23,631
ESPP contributions	4,004		2,672
Deferred rent	—		1,418
VAT liability	2,528		2,217
Acquisition holdback	2,240		—
Accrued other expense	22,140		18,054
Total accrued expenses and other current liabilities	$	117,625	$	96,343

Other long-term liabilities consisted of the following (in thousands):



	As of June 30, 2019		As of December 31, 2018
Deferred rent	$	—	$	7,569
Deferred tax liability	9,077		5,181
Acquisition holdback	4,280		2,290
Capital lease obligation	—		2,170
Accrued other expense	2,122		959
Total other long-term liabilities	$	15,479	$	18,169

Notes Payable

6 Months Ended

Jun. 30, 2019

Long-term Debt, Unclassified [Abstract]

Notes Payable

(a) Convertible Senior Notes and Capped Call Transactions

In May 2018, the Company issued $550.0 million aggregate principal amount of 0.25% convertible senior notes due 2023 in a private placement, including $75.0 million aggregate principal amount of such Notes pursuant to the exercise in full of the over-allotment options of the initial purchasers (collectively, the “Notes”). The interest on the Notes is payable semi-annually in arrears on June 1 and December 1 of each year, beginning on December 1, 2018.

The Notes may bear special interest under specified circumstances relating to the Company’s failure to comply with its reporting obligations under the indenture relating to the issuance of Notes (the “indenture”) or if the Notes are not freely tradeable as required by the indenture. The Notes will mature on June 1, 2023, unless earlier repurchased or redeemed by the Company or converted pursuant to their terms. The total net proceeds from the debt offering, after deducting initial purchaser discounts and debt issuance costs, paid or payable by us, were approximately $537.0 million.

Each $1,000 principal amount of the Notes is initially convertible into 14.1040 shares of the Company’s Class A common stock par value $0.001, which is equivalent to an initial conversion price of approximately $70.90 per share. The conversion rate is subject to adjustment upon the occurrence of certain specified events but will not be adjusted for any accrued and unpaid special interest. In addition, upon the occurrence of a make-whole fundamental change, as defined in the indenture, the Company will, in certain circumstances, increase the conversion rate by a number of additional shares for a holder that elects to convert its Notes in connection with such make-whole fundamental change or during the relevant redemption period.

Prior to the close of business on the business day immediately preceding March 1, 2023, the Notes may be convertible at the option of the holders only under the following circumstances:

(1) during any calendar quarter commencing after September 30, 2018, and only during such calendar quarter, if the last reported sale price of the Class A common stock for at least 20 trading days (whether or not consecutive) in a

period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is more than or equal to 130% of the conversion price on each applicable trading day;

(2) during the five business days period after any five consecutive trading day period in which, for each trading day of that period, the trading price per $1,000 principal amount of Notes for such trading day was less than 98% of the product of the last reported sale price of the Class A common stock and the conversion rate on each such trading day;

(3) upon the Company’s notice that it is redeeming any or all of the Notes; or

(4) upon the occurrence of specified corporate events.

On or after March 1, 2023, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders of the Notes may, at their option, convert all or a portion of their Notes regardless of the foregoing conditions.

Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of Class A common stock, or a combination of cash and shares of Class A Common Stock, at the Company’s election. It is the Company’s current intent to settle the principal amount of the Notes with cash.

During the three months ended June 30, 2019, the conditional conversion feature of the Notes was triggered as the last reported sale price of the Company's Class A common stock was more than or equal to 130% of the conversion price for at least 20 trading days (whether or not consecutive) in the period of 30 consecutive trading days ending on June 28, 2019 (the last trading day of the calendar quarter), and therefore the Notes are currently convertible, in whole or in part, at the option of the holders between July 1, 2019 through September 30, 2019. Whether the Notes will be convertible following such period will depend on the continued satisfaction of this condition or another conversion condition in the future. The Company may redeem the Notes, in whole or in part, at its option, on or after June 1, 2021 but before the 35th scheduled trading day before the maturity date, at a cash redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest, if any, if the last reported sale price of the Class A Common Stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading days ending on, and including, the trading day immediately before the date the redemption notices were sent; and the trading day immediately before such notices were sent.

No sinking fund is provided for the Notes. Upon the occurrence of a fundamental change (as defined in the indenture) prior to the maturity date, holders may require the Company to repurchase all or a portion of the Notes for cash at a price equal to 100% of the principal amount of the Notes to be repurchased, plus any accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

The Notes are senior unsecured obligations and will rank senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the Notes; equal in right of payment with the Company’s existing and future liabilities that are not so subordinated; effectively subordinated to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade payables) of current or future subsidiaries of the Company.

The foregoing description is qualified in its entirety by reference to the text of the indenture and the form of 0.25% convertible senior notes due 2023, which were filed as exhibits to the Company's Quarterly Report on Form 10-Q for the quarter ended June 30, 2018 and are incorporated herein by reference.

In accounting for the issuance of the Notes, the Company separated the Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar debt instrument that does not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was $119.4 million and was determined by deducting the fair value of the liability component from the par value of the Notes. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. The excess of the principal amount of the liability component over its carrying amount, or the debt discount, is amortized to interest expense at an annual effective interest rate of 5.7% over the contractual terms of the Notes.

In accounting for the transaction costs related to the Notes, the Company allocated the total amount incurred to the liability and equity components of the Notes based on the proportion of the proceeds allocated to the debt and equity components. Issuance costs attributable to the liability component were approximately $10.2 million, were recorded as an

additional debt discount and are amortized to interest expense using the effective interest method over the contractual terms of the Notes. Issuance costs attributable to the equity component were netted with the equity component in stockholders’ equity.

The net carrying amount of the liability component of the Notes was as follows (in thousands):



	As of June 30, 2019			As of December 31, 2018
Principal	$	550,000		$	550,000
Unamortized discount	(95,719		)	(106,484		)
Unamortized issuance costs	(8,104		)	(9,020		)
Net carrying amount	$	446,177		$	434,496

The net carrying amount of the equity component of the Notes was as follows (in thousands):



	As of June 30, 2019			As of December 31, 2018
Proceeds allocated to the conversion options (debt discount)	$	119,435		$	119,435
Issuance costs	(2,819		)	(2,819		)
Net carrying amount	$	116,616		$	116,616

The following table sets forth the interest expense recognized related to the Notes (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Contractual interest expense	$	344	$	164	$	688	$	164
Amortization of debt issuance costs	458		211		916		211
Amortization of debt discount	5,383		2,484		10,766		2,484
Total interest expense related to the Notes	$	6,185	$	2,859	$	12,370	$	2,859

In connection with the offering of the Notes, the Company entered into privately-negotiated capped call transactions with certain counterparties (the “capped calls”). The capped calls each have an initial strike price of approximately $70.90 per share, subject to certain adjustments, which corresponds to the initial conversion price of the Notes. The capped calls have initial cap prices of $105.04 per share, subject to certain adjustments. The capped calls cover, subject to anti-dilution adjustments, approximately 7,757,200 shares of Class A Common Stock. The capped calls are generally intended to reduce or offset the potential dilution to the Class A Common Stock upon any conversion of the Notes with such reduction or offset, as the case may be, subject to a cap based on the cap price. The capped calls expire on the earlier of (i) the last day on which any convertible securities remain outstanding and (ii) June 1, 2023, subject to earlier exercise. The capped calls are subject to either adjustment or termination upon the occurrence of specified extraordinary events affecting the Company, including a merger event, a tender offer, and a nationalization, insolvency or delisting involving the Company. In addition, the capped calls are subject to certain specified additional disruption events that may give rise to a termination of the capped calls, including changes in law, insolvency filings, and hedging disruptions. The capped call transactions are recorded in stockholders’ equity and are not accounted for as derivatives. The net cost of $58.5 million incurred to purchase the capped call transactions was recorded as a reduction to additional paid-in capital in the accompanying condensed consolidated balance sheet.

(b) Note Payable

In connection with the SendGrid acquisition, the Company assumed a note payable that was an arrangement of SendGrid with a financing company to acquire software and related professional services in exchange for a note payable. As of June 30, 2019, the outstanding balance on the note payable was $4.4 million and is recorded in the current and long term liabilities and the related software is included in property and equipment, net, in the accompanying condensed consolidated balance sheet. The note payable bears effective interest at 6.6% per annum compounded monthly and matures in August 2021. Principal and interest payments of are as follows:



Year Ending December 31:	Principal		Interest
2019 (remaining six months)	$	1,036	$	129
2020	2,176		153
2021	1,144		22
Total payments related to the note	$	4,356	$	304

Supplemental Balance Sheet Information

6 Months Ended

Jun. 30, 2019

Receivables [Abstract]

Supplemental Balance Sheet Information

A roll‑forward of the Company’s reserves is as follows (in thousands):

(a)Allowance for doubtful accounts:



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Balance, beginning of period	$	4,281		$	1,404		$	4,945		$	1,033
Additions	685			1,140			381			1,515
Assumed in acquisition	—			—			59			—
Write-offs	(193		)	(8		)	(612		)	(12		)
Balance, end of period	$	4,773		$	2,536		$	4,773		$	2,536

(b)Sales credit reserve:



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Balance, beginning of period	$	2,831		$	1,702		$	3,015		$	1,761
Additions	2,862			1,544			5,266			2,651
Assumed in acquisition	—			—			277			—
Deductions against reserve	(2,617		)	(621		)	(5,482		)	(1,787		)
Balance, end of period	$	3,076		$	2,625		$	3,076		$	2,625

Revenue by Geographic Area

6 Months Ended

Jun. 30, 2019

Revenue from Contract with Customer [Abstract]

Revenue by Geographic Area

Revenue by geographic area is based on the IP address or the mailing address at the time of registration. The following table sets forth revenue by geographic area (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Revenue by geographic area:
United States	$	194,998	$	111,244	$	361,551	$	209,879
International	80,041		36,510		146,627		66,991
Total	$	275,039	$	147,754	$	508,178	$	276,870



Percentage of revenue by geographic area:
United States	71	%	75	%	71	%	76	%
International	29	%	25	%	29	%	24	%

Long-lived assets outside the United States were not significant.

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies (a)Lease and Other Commitments The Company entered into various non-cancelable operating lease agreements for its facilities that expire over the next 10 years. See Note 5 to these condensed consolidated financial statements for additional detail on the Company's operating and finance lease commitments. In the three and six months ended June 30, 2019, the Company entered into several non-cancelable vendor agreements with terms from one to four years for a total purchase commitment of $9.7 million and $11.1 million, respectively. Additionally, as a result of its acquisition of SendGrid, the Company assumed a non-cancelable cloud services vendor contract that as of June 30, 2019, had a remaining value of $21.8 million and a remaining term of 2.9 years. (b)Legal Matters On April 30, 2015 and March 28, 2016, Telesign Corporation ("Telesign") filed lawsuits (which were subsequently consolidated) against the Company in the United States District Court, Central District of California (“Telesign I/II”). Telesign alleges in Telesign I/II that the Company is infringing four U.S. patents that it holds: U.S. Patent No. 7,945,034 (“034”), U.S. Patent No. 8,462,920 (“920”), U.S. Patent No. 8,687,038 (“038”) and U.S. Patent No. 9,300,792 (“792”). The consolidated Telesign I/II actions have been transferred to the United States District Court, Northern District. The patent infringement allegations in the lawsuit relate to the Company’s two-factor authentication use case, Authy and an API tool to find information about a phone number. Telesign seeks, among other things, to enjoin us from allegedly infringing the patents, along with damages for lost profits and damages based on a reasonable royalty. On March 8, 2017, in response to a petition by the Company, the U.S. Patent and Trademark Officer (“PTO”) issued an order instituting an inter partes review for the ‘792 patent. On March 6, 2018, the PTO found all claims challenged by the Company in the inter partes review unpatentable. Telesign did not appeal the PTO’s decision, and it is final. On October 19, 2018, the district court granted the Company's motion that all remaining asserted claims of the asserted patents are invalid under 35 U.S.C. §101 and entered judgment in the Company’s favor. On November 8, 2018, Telesign appealed the judgment to the United States Court of Appeals for the Federal Circuit where the case is now pending. Based on, among other things, final judgment being entered by the district court in the Company’s favor, the Company does not believe a loss is reasonably possible or estimable. On December 1, 2016, the Company filed a patent infringement lawsuit against Telesign in the United States District Court, Northern District of California (“Telesign III”), alleging infringement of United States Patent No. 8,306,021 (“021”), United States Patent No. 8,837,465 (“465”), United States Patent No. 8,755,376 (“376”), United States Patent No. 8,736,051 (“051”), United States Patent No. 8,737,962 (“962”), United States Patent No. 9,270,833 (“833”), and United States Patent No. 9,226,217 (“217”). Telesign filed a motion to dismiss the complaint on January 25, 2017. In two orders, issued on March 31, 2017 and April 17, 2017, the court granted Telesign’s motion to dismiss with respect to the ‘962, ‘833, ‘051 and ‘217 patents, but denied Telesign’s motion to dismiss as to the ‘021, ‘465 and ‘376 patents. On August 23, 2017, Telesign petitioned the PTO for inter partes review of the ‘021, ‘465, and ‘376 patents. On March 9, 2018, the PTO denied Telesign’s petition for inter partes review of the ‘021 patent and granted Telesign’s petitions for inter partes review of the ‘465 and ‘376 patents. On March 6, 2019, the PTO found all claims challenged by Telesign in the inter partes review unpatentable. The Company has appealed the decisions to the United States Court of Appeals for the Federal Circuit. Telesign III is currently stayed pending resolution of the inter partes reviews (and appeals from them) of the ‘465 and ‘376 patents. The Company is seeking a judgment of infringement, a judgment of willful infringement, monetary and injunctive relief, enhanced damages, and an award of costs and expenses against Telesign. On February 18, 2016, a putative class action complaint was filed in the Alameda County Superior Court in California, entitled Angela Flowers v. Twilio Inc. The complaint alleges that the Company’s products permit the interception, recording and disclosure of communications at a customer’s request and are in violation of the California Invasion of Privacy Act. The complaint seeks injunctive relief as well as monetary damages. On January 2, 2018, the court issued an order granting in part and denying in part the plaintiff’s class certification motion. The court certified two classes of individuals who, during specified time periods, allegedly sent or received certain communications involving the accounts of three of the Company’s customers that were recorded. Following mediation, on January 7, 2019, the parties signed a long form settlement agreement, providing for a payment of $10.0 million into a common fund and injunctive relief involving certain updates to Twilio’s Acceptable Use Policy and customer documentation. On January 15, 2019, the court entered an order granting preliminary approval of the settlement, and the parties signed an amended settlement agreement to conform to the court’s order. The court entered a final order and judgment approving the settlement on June 17, 2019. A final compliance hearing has been scheduled for February 25, 2020. Given insurance coverage, the Company continues to estimate its potential liability in the Flowers matter to be $1.7 million and carries this reserved amount in its condensed consolidated balance sheet as of June 30, 2019. On September 1, 2015, Twilio was named as a defendant in a First Amended Complaint in a putative class action captioned Jeremy Bauman v. David Saxe, et al. pending in the United States District Court, District of Nevada relating to the alleged sending of unsolicited text messages to the plaintiffs and putative class members. The Company filed a motion to dismiss, which was granted, and on September 20, 2016 the plaintiff filed a Second Amended Complaint with additional allegations that the Company violated the Telephone Consumer Protection Act (“TCPA”), and the Nevada Deceptive Trade Practices Act (“NDTPA”), NRS 41.600(2)(e). On January 10, 2019, the court granted Plaintiffs’ motion for class certification under the TCPA and denied plaintiff’s request to certify a class under the NDTPA. On February 13, 2019, the court issued an order denying the Company’s motion to dismiss as to Plaintiffs’ TCPA claim and granting dismissal as to Plaintiffs’ NDTPA claim. On February 22, 2019, the court stayed the case and directed all parties to mediation, which was conducted on May 15, 2019. On May 17, 2019, the original defendants (the “Saxe Defendants”) and the Company entered an agreement, which among other things, obligates the Saxe Defendants to fully fund all monetary and non-monetary aspects of the settlement of the matter and to obtain the dismissal of the plaintiffs’ and the class’s claims against the Company with prejudice. On May 22, 2019 the plaintiffs and the Saxe Defendants filed a motion to stay the case noting that they had reached agreement on the material terms of a settlement and needed additional time to draft a settlement agreement for submission to the court for review and approval. The Company did not oppose that motion. Plaintiffs and the Saxe Defendants continue to negotiate an agreement for submittal to the court. Based on, among other things, the Company’s agreement with the Saxe Defendants, the Company does not believe a loss is reasonably possible or estimable. In addition to the litigation discussed above, from time to time, the Company may be subject to legal actions and claims in the ordinary course of business. The Company has received, and may in the future continue to receive, claims from third parties asserting, among other things, infringement of their intellectual property rights. Future litigation may be necessary to defend itself, its partners and its customers by determining the scope, enforceability and validity of third‑party proprietary rights, or to establish its proprietary rights. The results of any current or future litigation cannot be predicted with certainty, and regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources, and other factors. Legal fees and other costs related to litigation and other legal proceedings are expensed as incurred and are included in general and administrative expenses in the accompanying condensed consolidated statements of operations. (c)Indemnification Agreements The Company has signed indemnification agreements with all of its board members and executive officers. The agreements indemnify the board members and executive officers from claims and expenses on actions brought against the individuals separately or jointly with the Company for certain indemnifiable events. Indemnifiable Events generally mean any event or occurrence related to the fact that the board member or the executive officer was or is acting in his or her capacity as a board member or an executive officer for the Company or was or is acting or representing the interests of the Company. In the ordinary course of business and in connection with our financing and business combinations transactions, the Company enters into contractual arrangements under which it agrees to provide indemnification of varying scope and terms to business partners, customers and other parties with respect to certain matters, including, but not limited to, losses arising out of the breach of such agreements, intellectual property infringement claims made by third parties and other liabilities relating to or arising from the Company’s various products, or its acts or omissions. In these circumstances, payment may be conditional on the other party making a claim pursuant to the procedures specified in the particular contract. Further, the Company’s obligations under these agreements may be limited in terms of time and/or amount, and in some instances, the Company may have recourse against third parties for certain payments. The terms of such obligations may vary. As of June 30, 2019 and December 31, 2018, no material amounts were accrued. (d)Other Taxes The Company conducts operations in many tax jurisdictions throughout the United States. In many of these jurisdictions, non-income-based taxes, such as sales and use and telecommunications taxes are assessed on the Company’s operations. Prior to March 2017, the Company had not billed nor collected these taxes from its customers and, in accordance with U.S. GAAP, recorded a provision for its tax exposure in these jurisdictions when it was both probable that a liability had been incurred and the amount of the exposure could be reasonably estimated. These estimates included several key assumptions including, but not limited to, the taxability of the Company’s services, the jurisdictions in which its management believes it has nexus, and the sourcing of revenues to those jurisdictions. Starting in March 2017, the Company began collecting these taxes from customers in certain jurisdictions, and since then, has expanded the number of jurisdictions where these taxes are being collected. Effective January 2018, the Company began to collect taxes in one additional jurisdiction and accordingly, from January 2018, the Company is not recording an additional provision for its exposure for new activities in that jurisdiction. The Company expects to continue to expand the number of jurisdictions where these taxes will be collected in the future. Simultaneously, the Company was and continues to be in discussions with certain states regarding its prior state sales and other taxes, if any, that the Company may owe. As of June 30, 2019 and December 31, 2018, the liability recorded for these taxes was $26.1 million and $22.6 million, respectively. In the event other jurisdictions challenge management’s assumptions and analysis, the actual exposure could differ materially from the current estimates.

Stockholders' Equity

6 Months Ended

Jun. 30, 2019

Stockholders' Equity Note [Abstract]

Stockholders' Equity

Stockholders’ Equity

(a)Preferred Stock

As of June 30, 2019 and December 31, 2018 , the Company had authorized 100,000,000 shares of preferred stock, par value $0.001, of which no shares were issued and outstanding.

(b)Common Stock

As of June 30, 2019 and December 31, 2018, the Company had authorized 1,000,000,000 shares of Class A common stock and 100,000,000 shares of Class B common stock, each par value $0.001 per share. As of June 30, 2019 and December 31, 2018, 121,377,614 shares and 80,769,763 shares of Class A common stock and 14,384,746 shares and 19,310,465 shares of Class B common stock, respectively, were issued and outstanding. Holders of Class A and Class B common stock are entitled to one vote per share and 10 votes per share, respectively, and the shares of Class A common stock and Class B common stock are identical, except for voting and conversion rights.

The Company had reserved shares of common stock for issuance as follows:



	As of June 30, 2019	As of December 31, 2018
Stock options issued and outstanding	9,125,950	7,978,369
Nonvested restricted stock units issued and outstanding	8,926,529	8,262,902
Class A common stock reserved for Twilio.org	776,334	572,676
Stock-based awards available for grant under 2016 Plan	15,727,925	9,313,354
Stock-based awards available for grant under 2016 ESPP	3,984,686	3,092,779
Class A common stock reserved for the convertible senior notes	10,472,165	10,472,165
Total	49,013,589	39,692,245

(c) Public Equity Offering

In June 2019, the Company completed a public equity offering in which the Company sold 8,064,515 shares of its Class A common stock, which included 1,051,893 shares sold pursuant to the exercise by the underwriters of an option to purchase additional shares, at a public offering price of $124.00 per share. The Company received aggregate proceeds of $979.0 million after deducting underwriting discounts and offering expenses paid and payable by the Company.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

2008 Stock Option Plan

The Company maintained a stock plan, the 2008 Stock Option Plan, as amended and restated (the “2008 Plan”), which allowed the Company to grant incentive (“ISO”), non‑statutory (“NSO”) stock options and restricted stock units (“RSU”) to its employees, directors and consultants to participate in the Company’s future performance through stock‑based awards at the discretion of the board of directors. Under the 2008 Plan, options to purchase the Company’s common stock could not be granted at a price less than fair value in the case of ISOs and NSOs. Fair value was determined by the board of directors, in good faith, with input from valuation consultants. On June 22, 2016, the plan was terminated in connection with the Company’s IPO. Accordingly, no shares are available for future issuance under the 2008 Plan. The 2008 Plan continues to govern outstanding equity awards granted thereunder. The Company’s right of first refusal for outstanding equity awards granted under the 2008 Plan terminated upon completion of the IPO. Options granted include provisions for early exercisability.

2016 Stock Option Plan

The Company’s 2016 Stock Option and Incentive Plan (the “2016 Plan”) became effective on June 21, 2016. The 2016 Plan provides for the grant of ISOs, NSOs, restricted stock, RSUs, stock appreciation rights, unrestricted stock awards, performance share awards, dividend equivalent rights and cash-based awards to employees, directors and consultants of the Company. A total of 11,500,000 shares of the Company’s Class A common stock were initially reserved for issuance under the 2016 Plan. These available shares automatically increase each January 1, beginning on January 1, 2017, by 5% of the number of shares of the Company’s Class A and Class B common stock outstanding on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation committee. On January 1, 2019 and 2018, the shares available for grant under the 2016 Plan were automatically increased by 5,004,011 shares and 4,698,490 shares, respectively.

Under the 2016 Plan, the stock options are granted at a price per share not less than 100% of the fair market value per share of the underlying common stock on the date of grant. Under both plans, stock options generally expire 10 years from the date of grant and vest over periods determined by the board of directors. The vesting period for new-hire options and restricted stock units is generally a four-year term from the date of grant, at a rate of 25% after one year, then monthly or quarterly, respectively, on a straight-line basis thereafter. In July 2017, the Company began granting restricted stock units to existing employees that vest in equal quarterly installments over a four year service period.

SendGrid Equity Awards Assumed in Acquisition

In connection with its acquisition of SendGrid, the Company assumed all stock options and restricted stock units issued under SendGrid’s 2009, 2012 or 2017 Stock Incentive Plans that were outstanding on the date of acquisition. The assumed equity awards will continue to be outstanding and will be governed by the provisions of their respective plans. Additionally, the Company assumed shares of SendGrid common stock that were reserved and available for issuance under SendGrid's 2017 Equity Incentive Plan, on an as converted basis. These shares can be utilized for future equity grants under the Company’s 2016 Plan, to the extent permitted by New York Stock Exchange rules.

2016 Employee Stock Purchase Plan

The Company’s Employee Stock Purchase Plan (“2016 ESPP”) became effective on June 21, 2016. A total of 2,400,000 shares of the Company’s Class A common stock were initially reserved for issuance under the 2016 ESPP. These available shares will automatically increase each January 1, beginning on January 1, 2017, by the lesser of 1,800,000 shares of the common stock, 1% of the number of shares of the Company’s Class A and Class B common stock outstanding on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s compensation committee. On January 1, 2019 and 2018, the shares available for grant under the 2016 Plan were automatically increased by 1,000,802 shares and 939,698 shares, respectively.

The 2016 ESPP allows eligible employees to purchase shares of the Company’s Class A common stock at a discount of up to 15% through payroll deductions of their eligible compensation, subject to any plan limitations. Except for the initial offering period, the 2016 ESPP provides for separate six-month offering periods beginning in May and November of each fiscal year, starting in May 2017.

On each purchase date, eligible employees will purchase the Company’s stock at a price per share equal to 85% of the lesser of (i) the fair market value of the Company’s Class A common stock on the offering date or (ii) the fair market value of the Company’s Class A common stock on the purchase date.

In the three months ended June 30, 2019 and 2018, 108,895 and 201,581 shares of Class A common stock were purchased under the 2016 ESPP, respectively, and 101,885 shares are expected to be purchased in the fourth quarter of 2019. As of June 30, 2019, total unrecognized compensation cost related to the 2016 ESPP was $3.2 million, which will be amortized over a weighted-average period of 0.4 years.

Stock options activity under the 2008 Plan and 2016 Plan was as follows:

Stock Options



	Number of options outstanding		Weighted- average exercise price (per share)		Weighted- average remaining contractual term (in years)	Aggregate intrinsic value (in thousands)
Outstanding options as of December 31, 2018	7,423,369		$	16.07	6.80	$	534,640
Granted	905,180		118.41
Assumed in acquisition	2,978,555		14.91
Exercised	(2,590,384	)	9.75
Forfeited and canceled	(145,770	)	26.12
Outstanding options as of June 30, 2019	8,570,950		$	28.21	7.05	$	926,868
Options vested and exercisable as of June 30, 2019	4,783,817		$	11.50	6.03	$	597,243

Aggregate intrinsic value represents the difference between the fair value of the Company’s Class A common stock as reported on the New York Stock Exchange and the exercise price of outstanding “in-the-money” options. The aggregate intrinsic value of stock options exercised was $100.8 million and $287.8 million in the three and six months ended June 30, 2019, respectively, and $43.4 million and $74.5 million in the three and six months ended June 30, 2018, respectively.

The total estimated grant date fair value of options vested was $19.5 million and $42.5 million in the three and six months ended June 30, 2019, respectively, and $4.8 million and $12.8 million in three and six months ended June 30, 2018, respectively.

The weighted-average grant-date fair value of options granted was $63.4 and $58.2 in the three and six months ended June 30, 2019, respectively, and $19.1 and $15.7 in the three and six months ended June 30, 2018, respectively.

On February 28, 2017, the Company granted a total of 555,000 shares of performance-based stock options in three distinct awards to an employee with grant date fair values of $13.48 , $10.26 and $8.41 per share for a total grant value of $5.9 million. The first half of each award vests upon satisfaction of a performance condition and the remainder vests thereafter in equal monthly installments over a two year period. The achievement window expires after 4.3 years from the date of grant and the stock options expire seven years after the date of grant. The stock options are amortized over a derived service period, as adjusted, of 3.1 years, 3.9 years and 4.6 years, respectively. The stock options value and the derived service period were estimated using the Monte-Carlo simulation model. The following table summarizes the details of the performance options:



	Number of options outstanding	Weighted- average exercise price (per share)		Weighted- average remaining contractual term (in years)	Aggregate intrinsic value (in thousands)
Outstanding options as of December 31, 2018	555,000	$	31.72	6.00	$	—
Granted	—	—
Exercised	—	—
Forfeited and canceled	—	—
Outstanding options as of June 30, 2019	555,000	$	31.72	4.67	$	58,070
Options vested and exercisable as of June 30, 2019	265,937	$	31.72	4.67	$	27,825

As of June 30, 2019, total unrecognized compensation cost related to nonvested stock options was $155.2 million, which will be amortized on a ratable basis over a weighted-average period of 2.2 years.

Restricted Stock Units



	Number of awards outstanding		Weighted- average grant date fair value (per share)		Aggregate intrinsic value (in thousands)
Nonvested RSUs as of December 31, 2018	8,262,902		$	42.70	$	729,373
Granted	1,886,838		125.14
Assumed in acquisition	561,999		112.88
Vested	(1,385,370	)	40.32
Forfeited and canceled	(399,840	)	$	54.13
Nonvested RSUs as of June 30, 2019	8,926,529		$	65.36	$	1,217,132

As of June 30, 2019, total unrecognized compensation cost related to nonvested RSUs was $532.0 million, which will be amortized over a weighted-average period of 2.9 years.

Valuation Assumptions

The fair value of employee stock options was estimated on the date of grant using the following assumptions in the Black-Scholes option pricing model:



	Three Months Ended June 30,		Six Months Ended June 30,
Employee Stock Options:	2019	2018	2019	2018
Fair value of common stock	$127.96	$41.22	$111.32 - $130.65	$33.01 - $41.22
Expected term (in years)	6.08	6.08	0.33 - 6.08	6.08
Expected volatility	49.19%	44.16%	48.31% - 66.46%	44.09% - 44.16%
Risk-free interest rate	2.44%	2.86%	2.39% - 2.51%	2.74% - 2.86%
Dividend rate	—%	—%	—%	—%



Employee Stock Purchase Plan:	Three Months Ended June 30,		Six Months Ended June 30,
	2019	2018	2019	2018
Expected term (in years)	0.50	0.50	0.50	0.50
Expected volatility	50.34%	39.78%	50.34%	39.78%
Risk-free interest rate	2.43%	2.09%	2.43%	2.09%
Dividend rate	—%	—%	—%	—%

The following assumptions were used in the Monte Carlo simulation model to estimate the grant date fair value and the derived service period of the performance options:



Asset volatility		40%
Equity volatility		45%
Discount rate		14%
Stock price at grant date		$31.72

Stock-Based Compensation Expense

The Company recorded the total stock-based compensation expense as follows (in thousands). In the three and six months ended June 30, 2019, the stock-based compensation expense associated with awards assumed in the SendGrid acquisition was $26.0 million and $46.7 million, respectively.



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of revenue	$	1,623	$	266	$	3,432	$	488
Research and development	33,701		9,749		59,040		17,621
Sales and marketing	14,564		5,049		26,313		8,908
General and administrative	20,852		5,942		40,279		11,529
Total	$	70,740	$	21,006	$	129,064	$	38,546

Net Loss Per Share Attributable to Common Stockholders

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

Basic and diluted net loss per common share is presented in conformity with the two-class method required for participating securities.

Class A and Class B common stock are the only outstanding equity in the Company. The rights of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to 10 votes per share. Shares of Class B common stock may be converted into Class A common stock at any time at the option of the stockholder and are automatically converted into Class A common stock upon sale or transfer, subject to certain limited exceptions.

Basic net loss per share attributable to common stockholders is computed using the weighted-average number of common shares outstanding during the period. Diluted net loss per share attributable to common stockholders is computed using the weighted-average number of common shares and, if dilutive, potential common shares outstanding during the period. The dilutive effect of these potential common shares is reflected in diluted earnings per share by application of the treasury stock method.

The following table sets forth the calculation of basic and diluted net loss per share attributable to common stockholders during the periods presented (in thousands, except share and per share data):



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Net loss attributable to common stockholders	$	(92,579	)	$	(24,006	)	$	(129,082	)	$	(47,735	)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	129,310,641			96,348,356			122,985,716			95,515,583
Net loss per share attributable to common stockholders, basic and diluted	$	(0.72	)	$	(0.25	)	$	(1.05	)	$	(0.50	)

The following outstanding shares of common stock equivalents were excluded from the calculation of the diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive:



	As of June 30,
	2019	2018
Stock options issued and outstanding	9,125,950	9,527,562
Nonvested restricted stock units issued and outstanding	8,926,529	7,705,589
Class A common stock reserved for Twilio.org	776,334	635,014
Class A common stock committed under 2016 ESPP	101,885	131,581
Conversion spread*	3,626,721	—
Unvested shares subject to repurchase	—	334
Total	22,557,419	18,000,080

_________

* Since the Company expects to settle the principal amount of its outstanding convertible senior notes in cash and any excess in shares of the Company's Class A common stock, the Company uses the treasury stock method for calculating any potential dilutive effect of the conversion spread on diluted net income per share, if applicable. The conversion spread will have a dilutive impact on diluted net income per share of Class A common stock when the average market price of the Company's Class A common stock for a given period exceeds the conversion price of $70.90 per share for the Notes. The conversion spread is calculated using the average market price of Class A common stock during the period, consistent with the treasury stock method.

Income Taxes

6 Months Ended

Jun. 30, 2019

Income Tax Disclosure [Abstract]

Income Taxes

The Company recorded the following income tax benefit (provision):



	Three Months Ended June 30,					Six Months Ended June 30,
	2019		2018			2019		2018
Income tax benefit (provision)	$	2,033	$	(150	)	$	53,754	$	(287	)

In connection with the SendGrid acquisition, the Company recorded a net deferred tax liability which provides an additional source of taxable income to support the realization of the pre-existing deferred tax assets and, accordingly, during the three and six months ended June 30, 2019, the Company released a total of $1.1 million and $52.7 million, respectively, of its U.S. valuation allowance. In the three months ended June 30, 2019, the Company also released $0.7 million of its valuation allowance in connection with its acquisition of Capio, Inc. The Company continues to maintain a valuation allowance for its U.S. Federal and state net deferred tax assets.

The provision for income taxes recorded in the three and six months ended June 30, 2018, consists primarily of income taxes and withholding taxes in foreign jurisdictions in which the Company conducts business. The Company’s U.S. operations have been in a loss position and the Company maintains a full valuation allowance against its U.S. deferred tax assets.

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in our Annual Report on Form 10-K filed with the SEC on March 1, 2019 (“Annual Report”). The condensed consolidated balance sheet as of December 31, 2018, included herein, was derived from the audited financial statements as of that date, but may not include all disclosures including certain notes required by U.S. GAAP on an annual reporting basis. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all normal recurring adjustments necessary to present fairly the financial position, results of operations, comprehensive loss and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2019 or any future period.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the Company and its wholly owned subsidiaries. All significant intercompany balances and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. These estimates are used for, but not limited to, revenue allowances and returns; recoverability of long-lived and intangible assets; capitalization and useful life of the Company’s capitalized internal-use software development costs; fair value of acquired intangible assets and goodwill; accruals and contingencies. Estimates are based on historical experience and on various assumptions that the Company believes are reasonable under current circumstances. However, future events are subject to change and best estimates and judgments may require further adjustments; therefore, actual results could differ materially from those estimates. Management periodically evaluates such estimates and they are adjusted prospectively based upon such periodic evaluation.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially expose the Company to a concentration of credit risk consist primarily of cash, cash equivalents, marketable securities, restricted cash and accounts receivable. The Company maintains cash, cash equivalents, marketable securities and restricted cash with financial institutions that management believes are financially sound and have minimal credit risk exposure although the balances will exceed insured limits. The Company sells its services to a wide variety of customers. If the financial condition or results of operations of any significant customers deteriorate substantially, operating results could be adversely affected. To reduce credit risk, management performs ongoing credit evaluations of the financial condition of significant customers. The Company does not require collateral from its credit customers and maintains reserves for estimated credit losses on customer accounts when considered necessary. Actual credit losses may differ from the Company’s estimates.
Deferred Revenue and Customer Deposits and Deferred Sales Commissions	Deferred Revenue and Customer Deposits Deferred revenue is recorded when cash payments are received in advance of future usage on non-cancelable contracts. Customer refundable prepayments are recorded as customer deposits. During the three and six months ended June 30, 2019, the Company recognized $4.7 million and $15.4 million of revenue, respectively, and during the three and six months ended June 30, 2018, the Company recognized $3.6 million and $7.2 million of revenue, respectively, that was included in the deferred revenue and customer deposits balance as of the beginning of the year. (f)Deferred Sales Commissions The Company records an asset for the incremental costs of obtaining a contract with a customer, for example, sales commissions that are earned upon execution of contracts. The Company uses the portfolio of data method to determine the estimated period of benefit of capitalized commissions which is determined to be five years. Amortization expense related to these capitalized costs related to initial contracts, upsells and renewals, is recognized on a straight line basis over the estimated period of benefit of the capitalized commissions.
Recently Accounting Guidance	Recently Adopted Accounting Guidance In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-02, "Leases (Topic 842)", which was further clarified in July 2018 by ASU 2018‑10, “Codification Improvements to Topic 842, Leases”, and ASU 2018‑11, “Leases-Targeted Improvements”. ASU 2018-10 provides narrow amendments to clarify how to apply certain aspects of the new lease standard. ASU 2018-11 addresses implementation issues related to the new lease standard. The standard is effective for interim and annual reporting periods beginning after December 15, 2018. Under the new standard, lessees are required to recognize in the balance sheet the right-of-use ("ROU") assets and lease liabilities that arise from operating leases. The Company adopted the standard using the optional alternative method on a prospective basis with an effective date as of the beginning of the Company’s fiscal year, January 1, 2019, and applied it to the operating leases that existed on that date. Prior year comparative financial information was not recast under the new standard and continues to be presented under ASC 840. The Company elected to utilize the package of practical expedients available for expired or existing contracts which allowed the Company to carryforward historical assessments of (a) whether contracts are or contain leases, (b) lease classification, and (c) initial direct costs. The Company elected the use of hindsight practical expedient in determining the lease term and assessing the likelihood that lease renewal, termination or purchase option will be exercised. The Company also elected to apply the short-term lease exception for all leases. Under the short-term lease exception, the Company will not recognize ROU assets or lease liabilities for leases that, at the acquisition date, have a remaining lease term of 12 months or less. As a result of implementing this guidance, the Company recognized a $123.5 million net operating ROU asset and a $132.0 million operating lease liability in its condensed consolidated balance sheet as of January 1, 2019. The ROU asset was presented net of deferred rent of $9.0 million as of January 1, 2019, in the accompanying condensed consolidated balance sheet and as a change within operating cash flows. In addition, on February 1, 2019, the Company acquired through its business combination with SendGrid approximately $33.7 million in operating ROU assets, $32.6 million in operating lease liability, $14.2 million in finance ROU assets and $13.6 million in finance lease liability. The Company measured the lease liability at the present value of the future lease payments as of January 1, 2019. The Company used its incremental borrowing rate to discount the lease payments. The Company derived the discount rate, adjusted for differences in the term and payment patterns, from the information available at the adoption date. The right-of-use asset is valued at the amount of the lease liability adjusted for the remaining December 31, 2018, balance of unamortized lease incentives, prepaid rent and deferred rent. The lease liability is subsequently measured at the present value of unpaid future lease payments as of the reporting date with a corresponding adjustment to the right-of-use asset. Absent a lease modification, the Company will continue to utilize the January 1, 2019, incremental borrowing rate. The Company recognizes lease costs on a straight-line basis and presents these costs as operating expenses within the consolidated statements of operations and comprehensive loss. The Company presents lease payments within the cash flows from operations within the consolidated statements of cash flows. The financial results for the three and six months ended June 30, 2019, are presented under the new standard, while the comparative periods presented are not adjusted and continue to be reported in accordance with the Company’s historical accounting policy. See Note 5, “Right-of-use Assets and Lease Liabilities” for further information. In March 2019, the FASB issued ASU 2019-01, “Codification Improvements” to Leases (Topic 842). This pronouncement did not have a material impact on the Company's financial statements. In August 2018, the FASB issued ASU 2018‑13, “Fair Value Measurement (Topic 820) Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement”. The amendments under ASU 2018‑13 remove, add and modify certain disclosure requirements on fair value measurements in ASC 820. The amendments are effective for interim and annual periods beginning after December 15, 2019. The Company early adopted this guidance effective April 1, 2019. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. In July 2018, the FASB issued ASU 2018-09, "Codification Improvements ", which does not prescribe any new accounting guidance, but instead makes minor improvements and clarifications of several topics. Certain updates are applicable immediately while others provide for a transition period to adopt as part of the next fiscal year beginning after December 15, 2018. The Company adopted this guidance effective April 1, 2019. The adoptions of this guidance did not have a material impact on the Company's consolidated financial statements. In January 2017, the FASB issued ASU 2017‑04, “Simplifying the Test for Goodwill Impairment”, which removes the second step of the goodwill impairment test that requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. This guidance is effective prospectively for interim and annual reporting periods beginning after December 15, 2019. The Company early adopted this guidance effective April 1, 2019. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. (h) Recently Issued Accounting Guidance, Not yet Adopted In August 2018, the FASB issued ASU 2018‑15, “Intangibles—Goodwill and Other—Internal‑Use Software (Subtopic 350‑40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract”. This standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal‑use software. The standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In June 2016, the FASB issued ASU 2016‑13, “Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments”, which changes the impairment model for most financial assets. The new model uses a forward‑looking expected loss method, which will generally result in earlier recognition of allowances for losses. In November 2018, the FASB issued ASU 2018‑19, “Codification Improvements to Topic 326, Financial Instruments—Credit Losses”, which clarifies that receivables arising from operating leases are not within the scope of Topic 326, Financial Instruments—Credit Losses. Instead, impairment of receivables arising from operating leases should be accounted for in accordance with Topic 842, Leases. In April 2019, the FASB issued ASU 2019-04, "Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments," which clarifies treatment of certain credit losses. In May 2019, the FASB issued ASU 2019-05, "Financial Instruments — Credit Losses (Topic 326): Targeted Transition Relief", which permits an entity, upon adoption of ASU 2016-13, to irrevocably elect the fair value option (on an instrument-by-instrument basis) for eligible financial assets measured at amortized cost basis. These ASUs are effective for annual and interim periods beginning after December 15, 2019, and early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of financial assets measured at fair value on a recurring basis

The following tables provide the financial assets measured at fair value on a recurring basis as of June 30, 2019, and December 31, 2018, (in thousands):



	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Fair Value Hierarchy as of June 30, 2019						Aggregate Fair Value
	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Level 1		Level 2		Level 3		Aggregate Fair Value
Financial Assets:
Cash and cash equivalents:
Money market funds	$	275,838	$	—	$	—		$	—		$	275,838	$	—	$	—	$	275,838
Reverse repurchase agreements	75,000		—		—			—			—		75,000		—		75,000
Commercial paper	114,471		—		—			—					114,471				114,471
Total included in cash and cash equivalents	465,309		—		—			—			275,838		189,471		—		465,309
Marketable securities:
U.S. Treasury securities	160,374		238		(1		)	—			160,611		—		—		160,611
Corporate debt securities and commercial paper	1,183,653		2,427		(309		)	(11		)	5,000		1,180,760		—		1,185,760
Total marketable securities	1,344,027		2,665		(310		)	(11		)	165,611		1,180,760		—		1,346,371
Strategic investment	5,000		—		—			—			—		—		5,000		5,000
Total financial assets	$	1,814,336	$	2,665	$	(310	)	$	(11	)	$	441,449	$	1,370,231	$	5,000	$	1,816,680



	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Fair Value Hierarchy as of December 31, 2018						Aggregate Fair Value
	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months			Level 1		Level 2		Level 3		Aggregate Fair Value
Financial Assets:
Cash and cash equivalents:
Money market funds	$	420,234	$	—	$	—		$	—		$	420,234	$	—	$	—	$	420,234
Reverse repurchase agreements	35,000		—		—			—			—		35,000		—		35,000
Commercial paper	9,983		—		—			—			—		9,983		—		9,983
Total included in cash and cash equivalents	465,217		—		—			—			420,234		44,983		—		465,217
Marketable securities:
U.S. Treasury securities	59,785		—		(7		)	(9		)	59,769		—		—		59,769
Corporate debt securities and commercial paper	201,683		23		(123		)	(224		)	—		201,359		—		201,359
Total marketable securities	261,468		23		(130		)	(233		)	59,769		201,359		—		261,128
Total financial assets	$	726,685	$	23	$	(130	)	$	(233	)	$	480,003	$	246,342	$	—	$	726,345

Schedule of contractual maturities of marketable securities

The following table summarizes the contractual maturities of marketable securities as of June 30, 2019, and December 31, 2018, (in thousands):



	As of June 30, 2019				As of December 31, 2018
	Amortized Cost		Aggregate Fair Value		Amortized Cost		Aggregate Fair Value
Financial Assets:
Less than one year	$	687,642	$	688,388	$	261,468	$	261,128
One to two years	656,385		657,983		—		—
Total	$	1,344,027	$	1,346,371	$	261,468	$	261,128

Property and Equipment (Tables)

6 Months Ended

Jun. 30, 2019

Property, Plant and Equipment [Abstract]

Schedule of property and equipment

Property and equipment consisted of the following (in thousands):



	As of June 30, 2019			As of December 31, 2018
Capitalized internal-use software development costs	$	85,145		$	72,647
Data center equipment ⁽¹⁾	14,795			—
Leasehold improvements	33,305			15,293
Office equipment	20,715			13,563
Furniture and fixtures ⁽¹⁾	7,273			4,918
Software	6,073			1,849
Total property and equipment	167,306			108,270
Less: accumulated depreciation and amortization	(60,826		)	(44,736		)
Total property and equipment, net	$	106,480		$	63,534

_______________


⁽¹⁾	Data center equipment and furniture and fixtures contain assets under finance leases. See Note 5 for further detail.

Right-of-Use Asset and Lease Liabilities (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Lease, Cost

The components of lease expense recorded in the condensed consolidated statement of operations were as follows (in thousands):



	Three Months Ended June 30, 2019		Six Months Ended June 30, 2019
Operating lease cost	$	8,273	$	15,446
Finance lease cost:
Amortization of assets	1,526		2,689
Interest on lease liabilities	189		337
Short-term lease cost	1,905		3,340
Variable lease cost	1,080		1,567
Total net lease cost	$	12,973	$	23,379

Supplemental cash flow and other information related to leases was as follows (in thousands):



	Six Months Ended June 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	12,145
Operating cash flows from finance leases	$	337
Financing cash flows from finance leases	$	2,463

Weighted average remaining lease term (in years):
Operating leases	6.8
Finance leases	3.1

Weighted average discount rate:
Operating leases	5.8		%
Finance leases	5.2		%

Assets and Liabilities, Lessee

Supplemental balance sheet information related to leases was as follows (in thousands):



Leases	Classification	As of June 30, 2019
Assets:
Operating lease assets	Operating right-of-use asset (a)	$	151,946
Finance lease assets	Property and equipment, net of accumulated depreciation (b)	12,970
Total leased assets		$	164,916

Liabilities:
Current
Operating	Operating lease liability, current	$	21,858
Finance	Financing lease liability, current	5,920
Noncurrent
Operating	Operating lease liability, noncurrent	138,819
Finance	Finance lease liability, noncurrent	7,752
Total lease liabilities		$	174,349


(a)	Operating lease assets are recorded net of accumulated amortization of $10.8 million as of June 30, 2019.

(b)

Finance lease assets are recorded net of accumulated depreciation of $2.7 million as of June 30, 2019.

Lessee, Operating Lease, Liability, Maturity

Maturities of lease liabilities were as follows (in thousands):



	As of June 30, 2019
	Operating Leases			Finance Leases
2019 (remaining six months)	$	14,523		$	3,278
2020	30,523			6,015
2021	28,791			3,130
2022	28,249			807
2023	27,762			413
Thereafter	68,106			1,316
Total lease payments	197,954			14,959
Less: imputed interest	(37,277		)	(1,287		)
Total lease obligations	160,677			13,672
Less: current obligations	(21,858		)	(5,920		)
Long-term lease obligations	$	138,819		$	7,752

Finance Lease, Liability, Maturity

Maturities of lease liabilities were as follows (in thousands):



	As of June 30, 2019
	Operating Leases			Finance Leases
2019 (remaining six months)	$	14,523		$	3,278
2020	30,523			6,015
2021	28,791			3,130
2022	28,249			807
2023	27,762			413
Thereafter	68,106			1,316
Total lease payments	197,954			14,959
Less: imputed interest	(37,277		)	(1,287		)
Total lease obligations	160,677			13,672
Less: current obligations	(21,858		)	(5,920		)
Long-term lease obligations	$	138,819		$	7,752

Schedule of Future Minimum Rental Payments for Operating Leases

Future minimum lease payment obligations under noncancelable operating and finance leases were as follows (in thousands):



	As of December 31, 2018
	Operating Leases		Finance Leases
2019	$	24,128	$	306
2020	29,527		512
2021	30,898		573
2022	30,492		590
2023	30,122		608
Thereafter	81,316		1,939
Total lease payments	$	226,483	$	4,528

Schedule of Future Minimum Lease Payments for Capital Leases

Future minimum lease payment obligations under noncancelable operating and finance leases were as follows (in thousands):



	As of December 31, 2018
	Operating Leases		Finance Leases
2019	$	24,128	$	306
2020	29,527		512
2021	30,898		573
2022	30,492		590
2023	30,122		608
Thereafter	81,316		1,939
Total lease payments	$	226,483	$	4,528

Business Combinations (Tables)

6 Months Ended

Jun. 30, 2019

Business Combinations [Abstract]

Purchase price components

The purchase price components, as adjusted, are summarized in the following table (in thousands):



	Total
Fair value of Class A common stock transferred	$	2,658,898
Fair value of the pre-combination service through equity awards	184,494
Total purchase price, as adjusted	$	2,843,392

Schedule of purchase price allocation

The following table presents the preliminary purchase price allocation recorded in the Company's condensed consolidated balance sheet as of June 30, 2019, (in thousands):



	Total
Net tangible liabilities assumed	$	(542	)
Intangible assets ⁽¹⁾	7,610
Goodwill ⁽²⁾	7,343
Total purchase price	$	14,411

_________________

⁽¹⁾ Identifiable finite-lived intangible assets were comprised of the following (in thousands):

⁽²⁾ The goodwill is primarily attributable to the future cash flows to be realized from the acquired technology. The goodwill is not deductible for U.S. tax purposes.

The following table presents the preliminary purchase price allocation, as adjusted, recorded in the Company's condensed consolidated balance sheet as of June 30, 2019 (in thousands). The Company expects to continue to obtain information to assist it in determining the fair values of the net assets acquired on the acquisition date during the measurement period:



	Total
Cash and cash equivalents	$	156,783
Accounts receivable and other current assets	11,636
Property and equipment, net	38,350
Operating right of use asset	33,742
Intangible assets	483,000
Other assets	1,664
Goodwill	2,238,070
Accounts payable and other liabilities	(11,115		)
Operating lease liability	(32,568		)
Financing lease liability	(13,616		)
Note payable	(5,387		)
Deferred tax liability	(57,167		)
Total purchase price	$	2,843,392

Schedule of identifiable finite-lived intangible assets

Identifiable intangible assets are comprised of the following (in thousands):



	Total		Estimated life (in years)
Developed technology and software	$	294,000	7
Customer relationships	169,000		7
Trade names	20,000		5
Total intangible assets acquired	$	483,000

Schedule of pro forma information

The following table presents the pro forma condensed combined financial information (in thousands):



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Revenue	$	275,039		$	183,429		$	521,924		$	345,114
Net loss attributable to common stockholders	$	(82,880	)	$	(53,858	)	$	(155,840	)	$	(73,339	)

Goodwill and Intangible Assets (Tables)

6 Months Ended

Jun. 30, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of goodwill balance

Goodwill balance as of June 30, 2019, and December 31, 2018, was as follows (in thousands):



	Total
Balance as of December 31, 2018	$	38,165
Goodwill additions related to 2019 acquisitions	2,246,398
Measurement period adjustments	(985		)
Balance as of June 30, 2019	$	2,283,578

Schedule of intangible assets

Intangible assets consisted of the following (in thousands):



	As of June 30, 2019
	Gross		Accumulated Amortization			Net
Amortizable intangible assets:
Developed technology	$	328,598	$	(30,581	)	$	298,017
Customer relationships	178,374		(13,280		)	165,094
Supplier relationships	2,696		(1,240		)	1,456
Trade names	20,060		(1,727		)	18,333
Patent	2,439		(224		)	2,215
Total amortizable intangible assets	532,167		(47,052		)	485,115
Non-amortizable intangible assets:
Domain names	32		—			32
Trademarks	263		—			263
Total	$	532,462	$	(47,052	)	$	485,410



	As of December 31, 2018
	Gross		Accumulated Amortization			Net
Amortizable intangible assets:
Developed technology	$	28,209	$	(10,497	)	$	17,712
Customer relationships	8,153		(2,411		)	5,742
Supplier relationships	2,696		(973		)	1,723
Trade name	60		(60		)	—
Patent	2,264		(178		)	2,086
Total amortizable intangible assets	41,382		(14,119		)	27,263
Non-amortizable intangible assets:
Domain names	32		—			32
Trademarks	263		—			263
Total	$	41,677	$	(14,119	)	$	27,558

Schedule of total estimated future amortization expense

Total estimated future amortization expense was as follows (in thousands):



	As of June 30, 2019
2019 (remaining six months)	$	39,878
2020	77,882
2021	76,371
2022	74,976
2023	72,786
Thereafter	143,222
Total	$	485,115

Accrued Expenses and Other Liabilities (Tables)

6 Months Ended

Jun. 30, 2019

Accrued Liabilities and Other Liabilities [Abstract]

Schedule of accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):



	As of June 30, 2019		As of December 31, 2018
Accrued payroll and related	$	15,717	$	9,886
Accrued bonus and commission	8,974		8,564
Accrued cost of revenue	34,523		29,901
Sales and other taxes payable	27,499		23,631
ESPP contributions	4,004		2,672
Deferred rent	—		1,418
VAT liability	2,528		2,217
Acquisition holdback	2,240		—
Accrued other expense	22,140		18,054
Total accrued expenses and other current liabilities	$	117,625	$	96,343

Schedule of other long-term liabilities

Other long-term liabilities consisted of the following (in thousands):



	As of June 30, 2019		As of December 31, 2018
Deferred rent	$	—	$	7,569
Deferred tax liability	9,077		5,181
Acquisition holdback	4,280		2,290
Capital lease obligation	—		2,170
Accrued other expense	2,122		959
Total other long-term liabilities	$	15,479	$	18,169

Notes Payable (Tables)

6 Months Ended

Jun. 30, 2019

Long-term Debt, Unclassified [Abstract]

Schedule of net carrying amount of the liability and equity components of the Notes

The net carrying amount of the liability component of the Notes was as follows (in thousands):



	As of June 30, 2019			As of December 31, 2018
Principal	$	550,000		$	550,000
Unamortized discount	(95,719		)	(106,484		)
Unamortized issuance costs	(8,104		)	(9,020		)
Net carrying amount	$	446,177		$	434,496

The net carrying amount of the equity component of the Notes was as follows (in thousands):



	As of June 30, 2019			As of December 31, 2018
Proceeds allocated to the conversion options (debt discount)	$	119,435		$	119,435
Issuance costs	(2,819		)	(2,819		)
Net carrying amount	$	116,616		$	116,616

Schedule of interest expense recognized related to the Notes

The following table sets forth the interest expense recognized related to the Notes (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Contractual interest expense	$	344	$	164	$	688	$	164
Amortization of debt issuance costs	458		211		916		211
Amortization of debt discount	5,383		2,484		10,766		2,484
Total interest expense related to the Notes	$	6,185	$	2,859	$	12,370	$	2,859

Schedule of principal and interest payments

Principal and interest payments of are as follows:



Year Ending December 31:	Principal		Interest
2019 (remaining six months)	$	1,036	$	129
2020	2,176		153
2021	1,144		22
Total payments related to the note	$	4,356	$	304

Supplemental Balance Sheet Information (Tables)

6 Months Ended

Jun. 30, 2019

Receivables [Abstract]

Schedule of the allowance for doubtful accounts

Allowance for doubtful accounts:



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Balance, beginning of period	$	4,281		$	1,404		$	4,945		$	1,033
Additions	685			1,140			381			1,515
Assumed in acquisition	—			—			59			—
Write-offs	(193		)	(8		)	(612		)	(12		)
Balance, end of period	$	4,773		$	2,536		$	4,773		$	2,536

Schedule of the sales credit reserve

Sales credit reserve:



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Balance, beginning of period	$	2,831		$	1,702		$	3,015		$	1,761
Additions	2,862			1,544			5,266			2,651
Assumed in acquisition	—			—			277			—
Deductions against reserve	(2,617		)	(621		)	(5,482		)	(1,787		)
Balance, end of period	$	3,076		$	2,625		$	3,076		$	2,625

Revenue by Geographic Area (Tables)

6 Months Ended

Jun. 30, 2019

Revenue from Contract with Customer [Abstract]

Schedule of revenue by geographic area

Revenue by geographic area is based on the IP address or the mailing address at the time of registration. The following table sets forth revenue by geographic area (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Revenue by geographic area:
United States	$	194,998	$	111,244	$	361,551	$	209,879
International	80,041		36,510		146,627		66,991
Total	$	275,039	$	147,754	$	508,178	$	276,870



Percentage of revenue by geographic area:
United States	71	%	75	%	71	%	76	%
International	29	%	25	%	29	%	24	%

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Stockholders' Equity Note [Abstract]

Schedule of reserved shares of common stock for issuance

The Company had reserved shares of common stock for issuance as follows:



	As of June 30, 2019	As of December 31, 2018
Stock options issued and outstanding	9,125,950	7,978,369
Nonvested restricted stock units issued and outstanding	8,926,529	8,262,902
Class A common stock reserved for Twilio.org	776,334	572,676
Stock-based awards available for grant under 2016 Plan	15,727,925	9,313,354
Stock-based awards available for grant under 2016 ESPP	3,984,686	3,092,779
Class A common stock reserved for the convertible senior notes	10,472,165	10,472,165
Total	49,013,589	39,692,245

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Stock-Based Compensation

Schedule of restricted stock unit activity



	Number of awards outstanding		Weighted- average grant date fair value (per share)		Aggregate intrinsic value (in thousands)
Nonvested RSUs as of December 31, 2018	8,262,902		$	42.70	$	729,373
Granted	1,886,838		125.14
Assumed in acquisition	561,999		112.88
Vested	(1,385,370	)	40.32
Forfeited and canceled	(399,840	)	$	54.13
Nonvested RSUs as of June 30, 2019	8,926,529		$	65.36	$	1,217,132

Schedule of valuation assumptions, options

The following assumptions were used in the Monte Carlo simulation model to estimate the grant date fair value and the derived service period of the performance options:



Asset volatility		40%
Equity volatility		45%
Discount rate		14%
Stock price at grant date		$31.72

Schedule of valuation assumptions, ESOP



Employee Stock Purchase Plan:	Three Months Ended June 30,		Six Months Ended June 30,
	2019	2018	2019	2018
Expected term (in years)	0.50	0.50	0.50	0.50
Expected volatility	50.34%	39.78%	50.34%	39.78%
Risk-free interest rate	2.43%	2.09%	2.43%	2.09%
Dividend rate	—%	—%	—%	—%

Schedule of stock based compensation expense

The Company recorded the total stock-based compensation expense as follows (in thousands). In the three and six months ended June 30, 2019, the stock-based compensation expense associated with awards assumed in the SendGrid acquisition was $26.0 million and $46.7 million, respectively.



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of revenue	$	1,623	$	266	$	3,432	$	488
Research and development	33,701		9,749		59,040		17,621
Sales and marketing	14,564		5,049		26,313		8,908
General and administrative	20,852		5,942		40,279		11,529
Total	$	70,740	$	21,006	$	129,064	$	38,546

Employee and nonemployee stock options

Stock-Based Compensation

Schedule of stock options activity

Stock Options



	Number of options outstanding		Weighted- average exercise price (per share)		Weighted- average remaining contractual term (in years)	Aggregate intrinsic value (in thousands)
Outstanding options as of December 31, 2018	7,423,369		$	16.07	6.80	$	534,640
Granted	905,180		118.41
Assumed in acquisition	2,978,555		14.91
Exercised	(2,590,384	)	9.75
Forfeited and canceled	(145,770	)	26.12
Outstanding options as of June 30, 2019	8,570,950		$	28.21	7.05	$	926,868
Options vested and exercisable as of June 30, 2019	4,783,817		$	11.50	6.03	$	597,243

Performance-based stock options

Stock-Based Compensation

Schedule of stock options activity

The following table summarizes the details of the performance options:



	Number of options outstanding	Weighted- average exercise price (per share)		Weighted- average remaining contractual term (in years)	Aggregate intrinsic value (in thousands)
Outstanding options as of December 31, 2018	555,000	$	31.72	6.00	$	—
Granted	—	—
Exercised	—	—
Forfeited and canceled	—	—
Outstanding options as of June 30, 2019	555,000	$	31.72	4.67	$	58,070
Options vested and exercisable as of June 30, 2019	265,937	$	31.72	4.67	$	27,825

Employee stock options

Stock-Based Compensation

Schedule of valuation assumptions, options

The fair value of employee stock options was estimated on the date of grant using the following assumptions in the Black-Scholes option pricing model:



	Three Months Ended June 30,		Six Months Ended June 30,
Employee Stock Options:	2019	2018	2019	2018
Fair value of common stock	$127.96	$41.22	$111.32 - $130.65	$33.01 - $41.22
Expected term (in years)	6.08	6.08	0.33 - 6.08	6.08
Expected volatility	49.19%	44.16%	48.31% - 66.46%	44.09% - 44.16%
Risk-free interest rate	2.44%	2.86%	2.39% - 2.51%	2.74% - 2.86%
Dividend rate	—%	—%	—%	—%

Net Loss Per Share Attributable to Common Stockholders (Tables)

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Schedule of the calculation of basic and diluted net loss per share attributable to common stockholders

The following table sets forth the calculation of basic and diluted net loss per share attributable to common stockholders during the periods presented (in thousands, except share and per share data):



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Net loss attributable to common stockholders	$	(92,579	)	$	(24,006	)	$	(129,082	)	$	(47,735	)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	129,310,641			96,348,356			122,985,716			95,515,583
Net loss per share attributable to common stockholders, basic and diluted	$	(0.72	)	$	(0.25	)	$	(1.05	)	$	(0.50	)

Schedule of common stock equivalents excluded from the computation of the diluted net loss per share attributable to common stockholders

The following outstanding shares of common stock equivalents were excluded from the calculation of the diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive:



	As of June 30,
	2019	2018
Stock options issued and outstanding	9,125,950	9,527,562
Nonvested restricted stock units issued and outstanding	8,926,529	7,705,589
Class A common stock reserved for Twilio.org	776,334	635,014
Class A common stock committed under 2016 ESPP	101,885	131,581
Conversion spread*	3,626,721	—
Unvested shares subject to repurchase	—	334
Total	22,557,419	18,000,080

_________

* Since the Company expects to settle the principal amount of its outstanding convertible senior notes in cash and any excess in shares of the Company's Class A common stock, the Company uses the treasury stock method for calculating any potential dilutive effect of the conversion spread on diluted net income per share, if applicable. The conversion spread will have a dilutive impact on diluted net income per share of Class A common stock when the average market price of the Company's Class A common stock for a given period exceeds the conversion price of $70.90 per share for the Notes. The conversion spread is calculated using the average market price of Class A common stock during the period, consistent with the treasury stock method.

Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounting Policies [Abstract]
Revenue recognized out of adjusted deferred revenue balance	$ 4.7	$ 3.6	$ 15.4	$ 7.2

Summary of Significant Accounting Policies - Deferred Sales Commissions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Deferred Sales Commissions
Total net capitalized costs	$ 17.5		$ 17.5		$ 9.4
Amortization of capitalized costs of obtaining a contract	$ 0.9	$ 0.3	$ 1.6	$ 0.5
Incremental commission costs of obtaining new contracts
Deferred Sales Commissions
Amortization period for deferred incremental commission costs of obtaining new contracts	5 years		5 years

Summary of Significant Accounting Policies - Recent Accounting Guidance (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Feb. 28, 2019	Feb. 01, 2019	Jan. 01, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Operating right of use asset	$ 151,946			$ 123,500	$ 0
Total lease obligations	$ 160,677			132,000
Deferred rent credit				$ 9,000
SendGrid
Business Acquisition [Line Items]
Operating right of use asset		$ 33,742	$ 33,700
Operating lease liability		32,568	32,600
Finance lease right of use asset			14,200
Financing lease liability		$ 13,616	$ 13,600

Fair Value Measurements - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($)	3 Months Ended
	Jun. 30, 2019	May 31, 2019	Dec. 31, 2018
Fair Value Measurements, Financial Assets
Cash and cash equivalents	$ 465,309,000		$ 465,217,000
Total amortized cost	1,344,027,000		261,468,000
Marketable securities, accumulated gross unrealized gain, before tax	2,665,000		23,000
Marketable securities, gross unrealized losses less than 12 months	(310,000)		(130,000)
Marketable securities, gross unrealized losses more than 12 months	(11,000)		(233,000)
Marketable securities, aggregate fair value	1,346,371,000		261,128,000
Strategic investment	5,000,000
Total financial assets, amortized cost or carrying value	1,814,336,000		726,685,000
Total financial assets	1,816,680,000		726,345,000
Note receivable		$ 5,000,000.0
Impairment of debt security	0
U.S. Treasury securities
Fair Value Measurements, Financial Assets
Total amortized cost	160,374,000		59,785,000
Marketable securities, accumulated gross unrealized gain, before tax	238,000
Marketable securities, gross unrealized losses less than 12 months	(1,000)		(7,000)
Marketable securities, gross unrealized losses more than 12 months			(9,000)
Marketable securities, aggregate fair value	160,611,000		59,769,000
Corporate debt securities and commercial paper
Fair Value Measurements, Financial Assets
Total amortized cost	1,183,653,000		201,683,000
Marketable securities, accumulated gross unrealized gain, before tax	2,427,000		23,000
Marketable securities, gross unrealized losses less than 12 months	(309,000)		(123,000)
Marketable securities, gross unrealized losses more than 12 months	(11,000)		(224,000)
Marketable securities, aggregate fair value	1,185,760,000		201,359,000
Level 1
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,838,000		420,234,000
Marketable securities, aggregate fair value	165,611,000		59,769,000
Total financial assets	441,449,000		480,003,000
Level 1 \| U.S. Treasury securities
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	160,611,000		59,769,000
Level 1 \| Corporate debt securities and commercial paper
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	5,000,000
Level 2
Fair Value Measurements, Financial Assets
Cash and cash equivalents	189,471,000		44,983,000
Marketable securities, aggregate fair value	1,180,760,000		201,359,000
Total financial assets	1,370,231,000		246,342,000
Level 2 \| U.S. Treasury securities
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	0
Level 2 \| Corporate debt securities and commercial paper
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	1,180,760,000		201,359,000
Level 3
Fair Value Measurements, Financial Assets
Strategic investment	5,000,000
Total financial assets	5,000,000
Carrying Value \| Money market funds
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,838,000		420,234,000
Carrying Value \| Reverse repurchase agreements
Fair Value Measurements, Financial Assets
Cash and cash equivalents	75,000,000		35,000,000
Carrying Value \| Commercial paper
Fair Value Measurements, Financial Assets
Cash and cash equivalents	114,471,000		9,983,000
Aggregate Fair Value \| Money market funds
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,838,000		420,234,000
Aggregate Fair Value \| Reverse repurchase agreements
Fair Value Measurements, Financial Assets
Cash and cash equivalents	75,000,000.0		35,000,000.0
Aggregate Fair Value \| Commercial paper
Fair Value Measurements, Financial Assets
Cash and cash equivalents	114,471,000		9,983,000
Aggregate Fair Value \| Level 1 \| Money market funds
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,838,000		420,234,000
Aggregate Fair Value \| Level 2 \| Reverse repurchase agreements
Fair Value Measurements, Financial Assets
Cash and cash equivalents	75,000,000		35,000,000
Aggregate Fair Value \| Level 2 \| Commercial paper
Fair Value Measurements, Financial Assets
Cash and cash equivalents	$ 114,471,000		$ 9,983,000

Fair Value Measurements - Marketable Securities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Marketable Securities
Other-than-temporary impairments associated with credit losses	$ 0		$ 0
Interest earned on marketable securities	2,600,000	$ 700,000	4,100,000	$ 1,400,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	465,309,000		465,309,000		$ 465,217,000
Aggregate Fair Value \| Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 75,000,000.0		$ 75,000,000.0		$ 35,000,000.0

Fair Value Measurements - Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Less than one year, amortized cost	$ 687,642	$ 261,468
One to two years, amortized cost	656,385	0
Total amortized cost	1,344,027	261,468
Less than one year, aggregate fair value	688,388	261,128
One to two years, aggregate fair value	657,983	0
Total aggregate fair value	$ 1,346,371	$ 261,128

Fair Value Measurements - Convertible Senior Notes (Details) - Convertible senior notes, 0.25%, due 2023 - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	May 31, 2018
Fair Value Measurements, Liabilities
Interest rate (as a percent)			0.25%
Level 2
Fair Value Measurements, Liabilities
Fair value of the notes	$ 1,116.2	$ 743.4

Property and Equipment - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property and Equipment
Total property and equipment	$ 167,306	$ 108,270
Less: accumulated depreciation and amortization	(60,826)	(44,736)
Total property and equipment, net	106,480	63,534
Capitalized internal-use software development costs
Property and Equipment
Total property and equipment	85,145	72,647
Data center equipment
Property and Equipment
Total property and equipment	14,795	0
Leasehold improvements
Property and Equipment
Total property and equipment	33,305	15,293
Office equipment
Property and Equipment
Total property and equipment	20,715	13,563
Furniture and fixtures
Property and Equipment
Total property and equipment	7,273	4,918
Software
Property and Equipment
Total property and equipment	$ 6,073	$ 1,849

Property and Equipment - Depreciation and Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 9.1	$ 4.3	$ 16.7	$ 8.5

Property and Equipment - Capitalized Software Development Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property and Equipment
Capitalized software development costs	$ 6,700	$ 6,700	$ 13,700	$ 13,100
Stock-based compensation capitalized in software development costs	1,600	1,500	3,244	2,909
Amortization of capitalized software development costs	$ 4,300	$ 3,000	$ 8,100	$ 5,700

Right-of-Use Asset and Lease Liabilities - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Number of leased properties \| property		19
Renewal option		5 years
Operating leases, rent expense	$ 2.1		$ 4.2
Minimum
Lessee, Lease, Description [Line Items]
Term of lease		1 year
Maximum
Lessee, Lease, Description [Line Items]
Term of lease		10 years
Leases Commencing Q3 2019
Lessee, Lease, Description [Line Items]
Operating lease, not yet commenced, liability		$ 1.8
Operating lease, not yet commenced, term of contract		2 years
Leases Commencing Q2 2020
Lessee, Lease, Description [Line Items]
Operating lease, not yet commenced, liability		$ 43.6
Finance lease not yet commenced, liability		$ 0.7
Lease not yet commenced, term of contract		6 years 9 months 18 days

Right-of-Use Asset and Lease Liabilities - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating lease cost	$ 8,273	$ 15,446
Finance Lease, Cost [Abstract]
Amortization of assets	1,526	2,689
Interest on lease liabilities	189	337
Short-term lease cost	1,905	3,340
Variable lease cost	1,080	1,567
Total net lease cost	$ 12,973	$ 23,379

Right-of-Use Asset and Lease Liabilities - Balance Sheet Classification of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
ASSETS
Operating lease assets	$ 151,946	$ 123,500	$ 0
Finance lease assets	12,970
Total leased assets	164,916
Current liabilities:
Operating	21,858		0
Finance	5,920		0
Noncurrent liabilities
Operating	138,819		0
Finance	7,752		$ 0
Total lease liabilities	174,349
Operating lease accumulated amortization	10,800
Finance lease accumulated depreciation	$ 2,700

Right-of-Use Asset and Lease Liabilities - Supplemental Cash Flows (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 12,145
Operating cash flows from finance leases	337
Financing cash flows from finance leases	$ 2,463
Weighted Average Remaining Lease Term [Abstract]
Operating leases	6 years 9 months 18 days
Finance leases	3 years 1 month 6 days
Weighted Average Discount Rate [Abstract]
Operating leases	5.80%
Finance leases	5.20%

Right-of-Use Asset and Lease Liabilities - Lease Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Maturity Of Operating Lease Liabilities
2019 (remaining six months)	$ 14,523
2020	30,523
2021	28,791
2022	28,249
2023	27,762
Thereafter	68,106
Total lease payments	197,954
Less: imputed interest	(37,277)
Total lease obligations	160,677	$ 132,000
Less: current obligations	(21,858)		$ 0
Long-term lease obligations	138,819		0
Maturity Of Finance Lease Liabilities
2019 (remaining six months)	3,278
2020	6,015
2021	3,130
2022	807
2023	413
Thereafter	1,316
Total lease payments	14,959
Less: imputed interest	(1,287)
Total lease obligations	13,672
Less: current obligations	(5,920)		0
Long-term lease obligations	$ 7,752		$ 0

Right-of-Use Asset and Lease Liabilities - Lease Maturities Prior To Adoption of New Lease Standard (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Operating Leases
2019	$ 24,128
2020	29,527
2021	30,898
2022	30,492
2023	30,122
Thereafter	81,316
Total minimum lease payments	226,483
Finance Leases
2019	306
2020	512
2021	573
2022	590
2023	608
Thereafter	1,939
Total minimum lease payments	$ 4,528

Business Combinations - Consideration (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended			6 Months Ended
	Jun. 30, 2019	Feb. 28, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Acquisition
Amount held for tax liabilities	$ 200
Goodwill, purchase accounting adjustments						$ (2,843,392)	$ 0
Fair value of the pre-combination service through equity awards			$ (7,126)	$ 191,620
Release of valuation allowance on deferred tax assets			600			48,600
Capio
Acquisition
Total purchase price, as adjusted	14,400
Amount of purchase price placed into an escrow account	$ 4,000
Escrow effective period	18 months
Grants (in shares)	43,556
Aggregate value	$ 5,900		5,900			5,900
Weighted average remaining contractual term (in years)	3 years
Net deferred tax liability	$ 800		800			800
Acquisition related costs						800
Release of valuation allowance on deferred tax assets			700
SendGrid
Acquisition
Total purchase price, as adjusted		$ 2,843,392
Net deferred tax liability		$ 57,167
Acquisition related costs			500		$ 500	39,900	$ 12,900
Shares issuable as part of acquisition (in shares)		23,600,000
Fair value of Class A common stock transferred		$ 2,658,898
Goodwill, purchase accounting adjustments			7,100
Goodwill, transfers			7,000
Fair value of the pre-combination service through equity awards		$ 184,494
Revenues			45,900			74,500
General and administrative \| SendGrid
Acquisition
Acquisition related costs			$ 500			$ 12,900

Business Combinations - Purchase Price Allocation (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Feb. 28, 2019	Feb. 01, 2019	Dec. 31, 2018
Acquisition
Goodwill	$ 2,283,578			$ 38,165
Capio
Acquisition
Net tangible liabilities assumed	(542)
Intangible assets	7,610
Goodwill	7,343
Deferred tax liability	(800)
Total purchase price	14,411
SendGrid
Acquisition
Cash and cash equivalents		$ 156,783
Accounts receivable and other current assets		11,636
Property and equipment, net		38,350
Operating right of use asset		33,742	$ 33,700
Intangible assets	$ 483,000	483,000
Other assets		1,664
Goodwill		2,238,070
Accounts payable and other liabilities		(11,115)
Operating lease liability		(32,568)	(32,600)
Financing lease liability		(13,616)	$ (13,600)
Note payable		(5,387)
Deferred tax liability		(57,167)
Total purchase price		$ 2,843,392

Business Combinations - Identifiable Finite-lived Intangible Assets (Details) - USD ($) $ in Thousands	1 Months Ended
	Jun. 30, 2019	Feb. 28, 2019
Capio
Acquisition
Intangible assets	$ 7,610
Capio \| Developed technology
Acquisition
Intangible assets	$ 6,390
Estimated life (in years)	6 years
Capio \| Customer relationships
Acquisition
Intangible assets	$ 1,220
Estimated life (in years)	4 years
SendGrid
Acquisition
Intangible assets	$ 483,000	$ 483,000
SendGrid \| Developed technology
Acquisition
Intangible assets	294,000
Estimated life (in years)		7 years
SendGrid \| Customer relationships
Acquisition
Intangible assets	169,000
Estimated life (in years)		7 years
SendGrid \| Trade names
Acquisition
Intangible assets	$ 20,000
Estimated life (in years)		5 years

Business Combinations - Pro Forma Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Release of valuation allowance on deferred tax assets	$ 600		$ 48,600
Valuation allowance			53,502	$ 0
Revenue	275,039	$ 183,429	521,924	345,114
Net loss attributable to common stockholders	(82,880)	(53,858)	(155,840)	(73,339)
SendGrid
Business Acquisition [Line Items]
Acquisition related costs	500	$ 500	39,900	12,900
Valuation allowance	(2,600)			$ 53,500
SendGrid \| General and administrative
Business Acquisition [Line Items]
Acquisition related costs	$ 500		$ 12,900

Goodwill and Intangible Assets - Goodwill Rollforward (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Goodwill
Balance (beginning of period)	$ 38,165
Goodwill additions related to 2019 acquisitions	2,246,398
Measurement period adjustments	(985)
Balance (end of period)	$ 2,283,578

Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Amortizable intangible assets:
Gross	$ 532,167	$ 41,382
Accumulated Amortization	(47,052)	(14,119)
Net	485,115	27,263
Intangible assets, gross	532,462	41,677
Total	485,410	27,558
Domain names
Amortizable intangible assets:
Non-amortizable intangible assets:	32	32
Trademarks
Amortizable intangible assets:
Non-amortizable intangible assets:	263	263
Developed technology
Amortizable intangible assets:
Gross	328,598	28,209
Accumulated Amortization	(30,581)	(10,497)
Net	298,017	17,712
Customer relationships
Amortizable intangible assets:
Gross	178,374	8,153
Accumulated Amortization	(13,280)	(2,411)
Net	165,094	5,742
Supplier relationships
Amortizable intangible assets:
Gross	2,696	2,696
Accumulated Amortization	(1,240)	(973)
Net	1,456	1,723
Trade names
Amortizable intangible assets:
Gross	20,060	60
Accumulated Amortization	(1,727)	(60)
Net	18,333	0
Patent
Amortizable intangible assets:
Gross	2,439	2,264
Accumulated Amortization	(224)	(178)
Net	$ 2,215	$ 2,086

Goodwill and Intangible Assets - Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 19.3	$ 1.4	$ 32.9	$ 2.8

Goodwill and Intangible Assets - Total Estimated Future Amortization Expense (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Intangible Assets
2019 (remaining six months)	$ 39,878
2020	77,882
2021	76,371
2022	74,976
2023	72,786
Thereafter	143,222
Net	$ 485,115	$ 27,263

Accrued Expenses and Other Liabilities - Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Liabilities and Other Liabilities [Abstract]
Accrued payroll and related	$ 15,717	$ 9,886
Accrued bonus and commission	8,974	8,564
Accrued cost of revenue	34,523	29,901
Sales and other taxes payable	27,499	23,631
ESPP contributions	4,004	2,672
Deferred rent	0	1,418
VAT liability	2,528	2,217
Acquisition holdback	2,240	0
Accrued other expense	22,140	18,054
Total accrued expenses and other current liabilities	$ 117,625	$ 96,343

Accrued Expenses and Other Liabilities - Long-term Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Liabilities and Other Liabilities [Abstract]
Deferred rent	$ 0	$ 7,569
Deferred tax liability	9,077	5,181
Acquisition holdback	4,280	2,290
Capital lease obligation	0	2,170
Accrued other expense	2,122	959
Total other long-term liabilities	$ 15,479	$ 18,169

Notes Payable - Issuance (Details) - USD ($)	1 Months Ended
Notes Payable - Issuance (Details) - USD ($)	May 31, 2018	Jun. 30, 2019	Dec. 31, 2018
Convertible senior notes, 0.25%, due 2023
Debt Instrument [Line Items]
Aggregate principal amount		$ 550,000,000	$ 550,000,000.0
Interest rate (as a percent)	0.25%
Net proceeds from the debt offering	$ 537,000,000.0
Convertible senior notes, 0.25%, due 2023 - over-allotment
Debt Instrument [Line Items]
Aggregate principal amount	$ 75,000,000.0

Notes Payable - Terms (Details) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	May 31, 2018 USD ($) $ / shares	Jun. 30, 2019 USD ($) D $ / shares	Dec. 31, 2018 USD ($) $ / shares
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) \| $ / shares		$ 0.001
Effective percentage		5.70%
Common Class A
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001	$ 0.001	$ 0.001
Convertible senior notes, 0.25%, due 2023
Debt Instrument [Line Items]
Threshold trading days \| D		20
Consecutive trading period \| D		30
Minimum sale price of stock as a percentage of the conversion price		130.00%
Number of consecutive trading days of threshold Notes trading price for conversion eligibility to follow \| D		5
Trading price as a percentage of the product of common stock sale price and conversion rate		98.00%
Percentage of principal amount of the Notes		100.00%
Interest rate (as a percent)	0.25%
Carrying amount of equity component \| $		$ 119,435	$ 119,435
Debt issuance costs \| $	$ 10,200	$ 8,104	$ 9,020
Convertible senior notes, 0.25%, due 2023 \| Common Class A
Debt Instrument [Line Items]
Conversion ratio	14.1040
Capped calls
Debt Instrument [Line Items]
Initial strike price (in dollars per share) \| $ / shares	$ 70.90

Notes Payable - Net Carrying Amount (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	May 31, 2018
Net carrying amount of the equity component of the Notes
Issuance costs	$ (953)
Convertible senior notes, 0.25%, due 2023
Net carrying amount of the liability component of the Notes
Aggregate principal amount	550,000	$ 550,000	$ 550,000
Unamortized discount	(95,719)	(95,719)	(106,484)
Unamortized issuance costs	(8,104)	(8,104)	(9,020)	$ (10,200)
Net carrying amount	446,177	446,177	434,496
Net carrying amount of the equity component of the Notes
Proceeds allocated to the conversion options (debt discount)	119,435	119,435	119,435
Issuance costs		(2,819)	(2,819)
Net carrying amount	$ 116,616	$ 116,616	$ 116,616

Notes Payable - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest expense recognized related to the Notes
Amortization of debt issuance costs			$ 11,682	$ 2,695
Convertible senior notes, 0.25%, due 2023
Interest expense recognized related to the Notes
Contractual interest expense	$ 344	$ 164	688	164
Amortization of debt issuance costs	458	211	916	211
Amortization of debt discount	5,383	2,484	10,766	2,484
Total interest expense related to the Notes	$ 6,185	$ 2,859	$ 12,370	$ 2,859

Notes Payable - Capped Calls (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	May 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Capped calls
Net cost to purchase the transactions		$ 0	$ 58,465
Capped calls
Capped calls
Initial strike price (in dollars per share)	$ 70.90
Initial cap price (in dollars per share)	$ 105.04
Number of shares covered	7,757,200
Net cost to purchase the transactions	$ 58,500

Notes Payable - Note Payable (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Debt Instrument [Line Items]
Effective percentage	5.70%
SendGrid
Debt Instrument [Line Items]
Note payable	$ 4,400
Effective percentage	6.60%
Notes Payable
Principal
2019 (remaining six months)	$ 1,036
2020	2,176
2021	1,144
Net carrying amount	4,356
Interest
2019 (remaining six months)	129
2020	153
2021	22
Total interest	$ 304

Supplemental Balance Sheet Information - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allowance for doubtful accounts
Balance, beginning of period	$ 4,281	$ 1,404	$ 4,945	$ 1,033
Additions	685	1,140	381	1,515
Assumed in acquisition	0	0	59	0
Write-offs	(193)	(8)	(612)	(12)
Balance, end of period	$ 4,773	$ 2,536	$ 4,773	$ 2,536

Supplemental Balance Sheet Information - Sales Credit Reserve (Details) - Sales credit reserve - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Sales credit reserve
Balance, beginning of period	$ 2,831	$ 1,702	$ 3,015	$ 1,761
Additions	2,862	1,544	5,266	2,651
Assumed in acquisition	0	0	277	0
Deductions against reserve	(2,617)	(621)	(5,482)	(1,787)
Balance, end of period	$ 3,076	$ 2,625	$ 3,076	$ 2,625

Revenue by Geographic Area - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue by geographic area
Revenue	$ 275,039	$ 147,754	$ 508,178	$ 276,870
United States
Revenue by geographic area
Revenue	194,998	111,244	361,551	209,879
International
Revenue by geographic area
Revenue	$ 80,041	$ 36,510	$ 146,627	$ 66,991

Revenue by Geographic Area - Percentage of Revenue by Geographic Area (Details) - Revenue from Contract with Customer Benchmark - Geographic Concentration Risk	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
United States
Percentage of revenue by geographic area
Percentage of revenue (as a percent)	71.00%	75.00%	71.00%	76.00%
International
Percentage of revenue by geographic area
Percentage of revenue (as a percent)	29.00%	25.00%	29.00%	24.00%

Commitments and Contingencies - Other Commitments (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Feb. 28, 2019	Jun. 30, 2019	Jun. 30, 2019
Long-term Purchase Commitment [Line Items]
Total purchase commitments		$ 9.7	$ 11.1
SendGrid
Long-term Purchase Commitment [Line Items]
Purchase obligation	$ 21.8
Term of non-cancellable agreement	2 years 10 months 24 days
Minimum
Long-term Purchase Commitment [Line Items]
Term of lease		1 year	1 year
Term of non-cancellable agreement		2 years	2 years
Maximum
Long-term Purchase Commitment [Line Items]
Term of lease		10 years	10 years
Term of non-cancellable agreement		4 years	4 years

Commitments and Contingencies - Legal Matters (Details) $ in Millions	Jan. 07, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jan. 02, 2018 class
Legal Matters
Settlement awarded to other party	$ 10.0
Estimated probable loss		$ 1.7
Pending Litigation
Legal Matters
Number of classes of individuals who allegedly sent or received certain communications \| class			2
Number of customers' accounts involved in the complaint			3

Commitments and Contingencies - Indemnification Agreements (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Indemnification Agreements
Loss Contingencies [Line Items]
Amount accrued	$ 0	$ 0

Commitments and Contingencies - Other taxes (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Liability for uncertain tax positions	$ 26.1	$ 22.6

Stockholders' Equity - Preferred Stock (Details) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Preferred Stock
Preferred stock, authorized (in shares)	100,000,000	100,000,000
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0

Stockholders' Equity - Common Stock (Details)	Jun. 30, 2019 Vote $ / shares shares	Dec. 31, 2018 $ / shares shares	May 31, 2018 $ / shares
Common Stock
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001
Common Class A
Common Stock
Common stock, authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001	$ 0.001	$ 0.001
Common stock, issued (in shares)	121,377,614	80,769,763
Common stock, outstanding (in shares)	121,377,614	80,769,763
Votes per share \| Vote	1
Common Class B
Common Stock
Common stock, authorized (in shares)	100,000,000	100,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001	$ 0.001
Common stock, issued (in shares)	14,384,746	19,310,465
Common stock, outstanding (in shares)	14,384,746	19,310,465
Votes per share \| Vote	10

Stockholders' Equity - Common Stock Shares Reserved (Details) - shares	Jun. 30, 2019	Dec. 31, 2018
Stockholders' Equity
Total	49,013,589	39,692,245
2016 Stock Option and Incentive Plan
Stockholders' Equity
Stock-based awards available for grant under 2016 Plan	15,727,925	9,313,354
Common Class A
Stockholders' Equity
Class A common stock reserved for Twilio.org	776,334	572,676
Class A common stock reserved for the convertible senior notes	10,472,165	10,472,165
Stock options issued and outstanding
Stockholders' Equity
Stock options issued and outstanding	9,125,950	7,978,369
Nonvested restricted stock units issued and outstanding
Stockholders' Equity
Nonvested restricted stock units issued and outstanding	8,926,529	8,262,902
Class A common stock committed under 2016 ESPP
Stockholders' Equity
Stock-based awards available for grant under 2016 Plan	3,984,686	3,092,779

Stockholders' Equity Stockholders' Equity - Follow-on Public Offering (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Stock price at grant date (in dollars per share)	$ 124.00	$ 124.00	$ 124.00
Proceeds from a public offering, net of underwriting discount	$ 979,000		$ 980,000	$ 0
Common Class A \| Follow-on Public Offering
Class of Stock [Line Items]
Shares sold (in shares)	8,064,515	8,064,515
Common Class A \| Over-Allotment Option, FPO
Class of Stock [Line Items]
Shares sold (in shares)	1,051,893

Stock-Based Compensation - 2008 Stock Option Plan (Details)	Jun. 30, 2019 shares
2008 Stock Option Plan
Stock Based Compensation
Shares available for future issuance (in shares)	0

Stock-Based Compensation - 2016 Stock Option Plan (Details) - shares			6 Months Ended
	Jan. 01, 2019	Jan. 01, 2018	Jun. 30, 2019	Jun. 21, 2016
Stock Based Compensation
Increase in shares available for grant (in shares)	1,000,802	939,698
Employee and nonemployee stock options
Stock Based Compensation
Expiration term			10 years
Employee and nonemployee stock options \| New Hires
Stock Based Compensation
Vesting period			4 years
Employee and nonemployee stock options \| First vesting \| New Hires
Stock Based Compensation
Percentage of vesting rights			25.00%
Vesting period			1 year
Nonvested restricted stock units issued and outstanding
Stock Based Compensation
Vesting period			4 years
Nonvested restricted stock units issued and outstanding \| First vesting \| New Hires
Stock Based Compensation
Percentage of vesting rights			25.00%
Vesting period			1 year
2016 Stock Option and Incentive Plan
Stock Based Compensation
Maximum automatic annual increase as a percentage of outstanding common shares			5.00%
Increase in shares available for grant (in shares)	5,004,011	4,698,490
2016 Stock Option and Incentive Plan \| Common Class A
Stock Based Compensation
Shares reserved for issuance (in shares)				11,500,000
2016 Stock Option and Incentive Plan \| Employee and nonemployee stock options
Stock Based Compensation
Minimum grant price as a percentage of fair market value per share of the underlying common stock on the date of grant (as a percent)			100.00%

Stock-Based Compensation - 2016 Employee Stock Purchase Plan (Details) - USD ($) $ in Millions			3 Months Ended			6 Months Ended
	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 21, 2016
Stock Based Compensation
Increase in shares available for grant (in shares)	1,000,802	939,698
Unrecognized compensation cost, other than options				$ 3.2		$ 3.2
Weighted-average period (in years)						4 months 24 days
Class A common stock committed under 2016 ESPP
Stock Based Compensation
Maximum automatic annual increase as a percentage of outstanding common shares				1.00%		1.00%
Maximum automatic annual increase (in shares)				1,800,000		1,800,000
Common Class A \| Class A common stock committed under 2016 ESPP
Stock Based Compensation
Shares reserved for issuance (in shares)							2,400,000
Discount from market price, offering date (as a percent)						15.00%
Discount from market price, purchase date (as a percent)						15.00%
Purchase price, percentage of fair market value (as a percent)						85.00%
Shares purchased (in shares)				108,895	201,581
Scenario, Forecast
Stock Based Compensation
Shares purchased (in shares)			101,885

Stock-Based Compensation - Stock Option Activity (Details) - Employee and nonemployee stock options $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Number of options outstanding
Outstanding options as of the beginning of the period (in shares) \| shares	7,423,369
Granted (in shares) \| shares	905,180
Assumed in acquisition (in shares) \| shares	2,978,555
Exercised (in shares) \| shares	(2,590,384)
Forfeited and cancelled (in shares) \| shares	(145,770)
Outstanding options as of the end of the period (in shares) \| shares	8,570,950	7,423,369
Weighted- average exercise price (per share)
Outstanding options as of the beginning of the period (in dollars per share) \| $ / shares	$ 16.07
Granted (in dollars per share) \| $ / shares	118.41
Assumed in acquisition (in dollars per share) \| $ / shares	14.91
Exercised (in dollars per share) \| $ / shares	9.75
Forfeited and cancelled (in dollars per share) \| $ / shares	26.12
Outstanding options as of the end of the period (in dollars per share) \| $ / shares	$ 28.21	$ 16.07
Weighted- average remaining contractual term (in years)
Weighted-average remaining contractual term (in years)	7 years 18 days	6 years 9 months 18 days
Aggregate intrinsic value \| $	$ 926,868	$ 534,640
Options vested and exercisable and options vested and expected to vest
Options vested and exercisable - number of options outstanding (in shares) \| shares	4,783,817
Options vested and exercisable - weighted-average exercise price (in dollars per share) \| $ / shares	$ 11.50
Options vested and exercisable - weighted-average remaining contractual term	6 years 10 days
Options vested and exercisable - aggregate intrinsic value \| $	$ 597,243

Stock-Based Compensation - Stock Options - Additional Information (Details) - Employee and nonemployee stock options - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock Based Compensation
Aggregate intrinsic value of stock options exercised	$ 100.8	$ 43.4	$ 287.8	$ 74.5
Grant date fair value of options vested	$ 19.5	$ 4.8	$ 42.5	$ 12.8
Weighted-average grant date fair value of options granted (in dollars per share)	$ 63.4	$ 19.1	$ 58.2	$ 15.7

Stock-Based Compensation - Performance-Based Stock Options (Details) $ / shares in Units, $ in Thousands		6 Months Ended	12 Months Ended
	Feb. 28, 2017 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Performance-based stock options
Stock-Based Compensation
Number of distinct awards	3
Total grant value \| $	$ 5,900
Vesting period upon satisfaction of performance condition	2 years
Performance condition achievement window	4 years 3 months 18 days
Expiration term	7 years
Number of options outstanding
Outstanding options as of the beginning of the period (in shares) \| shares		555,000
Granted (in shares) \| shares	555,000	0
Exercised (in shares) \| shares		0
Forfeited and cancelled (in shares) \| shares		0
Outstanding options as of the end of the period (in shares) \| shares		555,000	555,000
Weighted- average exercise price (per share)
Outstanding options as of the beginning of the period (in dollars per share)		$ 31.72
Granted (in dollars per share)		0
Exercised (in dollars per share)		0
Forfeited and cancelled (in dollars per share)		0
Outstanding options as of the end of the period (in dollars per share)		$ 31.72	$ 31.72
Weighted-average remaining contractual term
Weighted-average remaining contractual term (in years)		4 years 8 months 1 day	6 years
Aggregate intrinsic value \| $		$ 58,070	$ 0
Options vested and exercisable
Options vested and exercisable - number of options outstanding (in shares) \| shares		265,937
Options vested and exercisable - weighted-average exercise price (in dollars per share)		$ 31.72
Options vested and exercisable - weighted-average remaining contractual term		4 years 8 months 1 day
Options vested and exercisable - aggregate intrinsic value \| $		$ 27,825
$13.48 grant date fair value
Stock-Based Compensation
Grant date fair value (in dollars per share)	$ 13.48
Derived service period as adjusted	3 years 1 month 6 days
$10.26 grant date fair value
Stock-Based Compensation
Grant date fair value (in dollars per share)	$ 10.26
Derived service period as adjusted	3 years 10 months 24 days
$8.41 grant date fair value
Stock-Based Compensation
Grant date fair value (in dollars per share)	$ 8.41
Derived service period as adjusted	4 years 7 months 6 days

Stock-Based Compensation - Stock Options - Unrecognized Compensation Cost (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Stock Based Compensation
Weighted-average period (in years)	4 months 24 days
Stock options issued and outstanding
Stock Based Compensation
Unrecognized compensation cost, options	$ 155.2
Weighted-average period (in years)	2 years 2 months 12 days

Stock-Based Compensation - Restricted Stock Units Activity (Details) - Nonvested restricted stock units issued and outstanding - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Number of awards outstanding
Nonvested RSUs at the beginning of the period (in shares)	8,262,902
Granted (in shares)	1,886,838
Assumed in SendGrid acquisition (in shares)	561,999
Vested (in shares)	(1,385,370)
Forfeited and canceled (in shares)	(399,840)
Nonvested RSUs at the end of the period (in shares)	8,926,529
Weighted- average grant date fair value (per share)
Nonvested RSUs at the beginning of the period (in dollars per share)	$ 42.70
Granted (in dollars per share)	125.14
Assumed in SendGrid acquisition (in dollars per share)	112.88
Vested (in dollars per share)	40.32
Forfeited and canceled (in dollars per share)	54.13
Nonvested RSUs at the end of the period (in dollars per share)	$ 65.36
Aggregate intrinsic value (in thousands)
Aggregate intrinsic value	$ 1,217,132	$ 729,373

Stock-Based Compensation - Restricted Stock Units - Unrecognized Compensation Cost (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Stock Based Compensation
Unrecognized compensation cost, other than options	$ 3.2
Weighted-average period (in years)	4 months 24 days
Nonvested restricted stock units issued and outstanding
Stock Based Compensation
Unrecognized compensation cost, other than options	$ 532.0
Weighted-average period (in years)	2 years 10 months 24 days

Stock-Based Compensation - Valuation Assumptions (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Valuation Assumptions
Stock price at grant date (in dollars per share)	$ 124.00		$ 124.00
Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)	$ 127.96	$ 41.22
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days		6 years 1 month 6 days
Expected volatility, low end of range (as a percent)	49.19%	44.16%	48.31%	44.09%
Expected volatility, high end of range (as a percent)	49.19%	44.16%	66.46%	44.16%
Risk-free interest rate, low end of range (as a percent)	2.44%	2.86%	2.39%	2.74%
Risk-free interest rate, high end of range (as a percent)	2.44%	2.86%	2.51%	2.86%
Dividend rate (as a percent)	0.00%	0.00%	0.00%	0.00%
Class A common stock committed under 2016 ESPP
Valuation Assumptions
Expected term (in years)	6 months	6 months	6 months	6 months
Expected volatility, high end of range (as a percent)	50.34%	39.78%	50.34%	39.78%
Risk-free interest rate, high end of range (as a percent)	2.43%	2.09%	2.43%	2.09%
Dividend rate (as a percent)	0.00%	0.00%	0.00%	0.00%
Performance-based stock options
Valuation Assumptions
Asset volatility (as a percent)			40.00%
Equity volatility (as a percent)			45.00%
Discount rate (as a percent)			14.00%
Stock price at grant date (in dollars per share)	$ 31.72		$ 31.72
Minimum \| Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)			$ 111.32	$ 33.01
Expected term (in years)			3 months 18 days
Maximum \| Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)			$ 130.65	$ 44.12
Expected term (in years)			6 years 1 month 6 days

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-Based Compensation Expense
Stock-based compensation expense	$ 70,740	$ 21,006	$ 129,064	$ 38,546
Cost of revenue
Stock-Based Compensation Expense
Stock-based compensation expense	1,623	266	3,432	488
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense	33,701	9,749	59,040	17,621
Sales and marketing
Stock-Based Compensation Expense
Stock-based compensation expense	14,564	5,049	26,313	8,908
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense	20,852	$ 5,942	40,279	$ 11,529
SendGrid
Stock-Based Compensation Expense
Stock-based compensation expense	$ 26,000		$ 46,700

Net Loss per Share Attributable to Common Stockholders - General Information (Details)	Jun. 30, 2019 Vote
Common Class A
Net Loss Per Share Attributable to Common Stockholders
Votes per share	1
Common Class B
Net Loss Per Share Attributable to Common Stockholders
Votes per share	10

Net Loss Per Share Attributable to Common Stockholders - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Loss Per Share Attributable to Common Stockholders
Net loss attributable to common stockholders	$ (92,579)	$ (24,006)	$ (129,082)	$ (47,735)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	129,310,641	96,348,356	122,985,716	95,515,583
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.72)	$ (0.25)	$ (1.05)	$ (0.50)

Net Loss Per Share Attributable to Common Stockholders - Anti-Dilutive Securities (Details) - $ / shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Anti-dilutive securities
Total	22,557,419	18,000,080
Conversion price (in dollars per share)	$ 70.90
Stock options issued and outstanding
Anti-dilutive securities
Total	9,125,950	9,527,562
Nonvested restricted stock units issued and outstanding
Anti-dilutive securities
Total	8,926,529	7,705,589
Class A common stock reserved for Twilio.org
Anti-dilutive securities
Total	776,334	635,014
Class A common stock committed under 2016 ESPP
Anti-dilutive securities
Total	101,885	131,581
Conversion spread
Anti-dilutive securities
Total	3,626,721	0
Unvested shares subject to repurchase
Anti-dilutive securities
Total	0	334

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income tax benefit (provision)	$ 2,033	$ (150)	$ 53,754	$ (287)
Decrease in valuation allowance	1,100		52,700
Valuation Allowance [Line Items]
Release of valuation allowance on deferred tax assets	600		$ 48,600
Capio
Valuation Allowance [Line Items]
Release of valuation allowance on deferred tax assets	$ 700

Estimated life
(in years)

Developed technology and software

Customer relationships

Total intangible assets acquired