Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 30, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
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	101 Spear Street
Entity Address, Address Line Two	First Floor
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
Title of 12(b) Security	Class A Common Stock, par value $0.001 per share
Trading Symbol	TWLO
Security Exchange Name	NYSE
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
Entity Central Index Key	0001447669
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Common Class A
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		128,731,012
Common Class B
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		11,321,940

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 345,518	$ 253,660
Short-term marketable securities	1,497,869	1,599,033
Accounts receivable, net	172,865	154,067
Prepaid expenses and other current assets	61,405	54,571
Total current assets	2,077,657	2,061,331
Restricted cash	0	75
Property and equipment, net	150,944	141,256
Operating right-of-use asset	159,439	156,741
Intangible assets, net	445,153	460,849
Goodwill	2,291,637	2,296,784
Other long-term assets	41,435	33,480
Total assets	5,166,265	5,150,516
Current liabilities:
Accounts payable	18,450	39,099
Accrued expenses and other current liabilities	195,393	147,681
Deferred revenue and customer deposits	26,706	26,362
Operating lease liability, current	29,949	27,156
Finance lease liability, current	6,539	6,924
Total current liabilities	277,037	247,222
Operating lease liability, noncurrent	140,120	139,200
Finance lease liability, noncurrent	7,250	8,746
Convertible senior notes, net	464,367	458,190
Other long-term liabilities	20,966	17,747
Total liabilities	909,740	871,105
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock	0	0
Class A and Class B common stock	139	138
Additional paid-in capital	5,034,278	4,952,999
Accumulated other comprehensive (loss) income	(4,289)	5,086
Accumulated deficit	(773,603)	(678,812)
Total stockholders’ equity	4,256,525	4,279,411
Total liabilities and stockholders’ equity	$ 5,166,265	$ 5,150,516

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Revenue	$ 364,868	$ 233,139
Cost of revenue	171,333	107,089
Gross profit	193,535	126,050
Operating expenses:
Research and development	114,339	77,855
Sales and marketing	116,722	71,607
General and administrative	55,170	64,176
Total operating expenses	286,231	213,638
Loss from operations	(92,696)	(87,588)
Other expenses, net	(1,118)	(636)
Loss before (provision) benefit for income taxes	(93,814)	(88,224)
(Provision) benefit for income taxes	(977)	51,721
Net loss attributable to common stockholders	$ (94,791)	$ (36,503)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.68)	$ (0.31)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)	139,231,594	116,590,513

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net loss	$ (94,791)	$ (36,503)
Other comprehensive income (loss):
Net unrealized (loss) gain on marketable securities, net of tax	(9,375)	1,041
Comprehensive loss attributable to common stockholders	$ (104,166)	$ (35,462)

Condensed Consolidated Statements of Stockholders Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock Common Class A	Common Stock Common Class B	Additional Paid In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
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)
Exercises of stock options (in shares)		748,679	1,023,984
Exercises of 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)
Equity awards assumed in acquisition	191,620			191,620
Net unrealized (loss) gain on marketable securities, net of tax	1,041				1,041
Shares issued in acquisition (in shares)		23,555,081
Shares issued in acquisition	2,658,898	$ 24		2,658,874
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, 2019		126,882,172	11,530,627
Balance at Dec. 31, 2019	4,279,411	$ 124	$ 14	4,952,999	5,086	(678,812)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(94,791)					(94,791)
Exercises of stock options (in shares)		243,029	426,001
Exercises of stock options	8,231			8,231
Vesting of restricted stock units (in shares)		849,763	23,107
Vesting of restricted stock units	1	$ 1
Value of equity awards withheld for tax liability (in shares)		(8,726)	(4,692)
Value of equity awards withheld for tax liability	(1,674)			(1,674)
Conversion of shares of Class B common stock into shares of Class A common stock (in shares)		618,103	(618,103)
Conversion of shares of Class B common stock into shares of Class A common stock		$ 1	$ (1)
Donated common stock (in shares)		22,102
Donated common stock	2,701			2,701
Net unrealized (loss) gain on marketable securities, net of tax	(9,375)				(9,375)
Stock-based compensation	72,021			72,021
Balance (in shares) at Mar. 31, 2020		128,606,443	11,356,940
Balance at Mar. 31, 2020	$ 4,256,525	$ 126	$ 13	$ 5,034,278	$ (4,289)	$ (773,603)

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (94,791)	$ (36,503)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	32,239	21,248
Non-cash reduction to the right-of-use asset	8,023	4,854
Amortization of debt discount and issuance costs	6,178	5,841
Stock-based compensation	69,025	58,324
Tax benefit related to release of valuation allowance	(162)	(51,644)
Allowance for credit losses	4,170	11
Value of donated common stock	2,701	0
Other adjustments	4,352	(444)
Changes in operating assets and liabilities:
Accounts receivable	(23,123)	(206)
Prepaid expenses and other current assets	(8,130)	(9,479)
Other long-term assets	(5,759)	(2,959)
Accounts payable	(20,803)	1,161
Accrued expenses and other current liabilities	44,840	4,348
Deferred revenue and customer deposits	589	377
Operating right of use liability	(7,008)	(1,784)
Long-term liabilities	3,194	(2,258)
Net cash provided by (used in) operating activities	15,535	(9,113)
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisitions, net of cash acquired, and other related payments	(2,377)	156,783
Purchases of marketable securities and other investments	(228,025)	(419,498)
Proceeds from sales and maturities of marketable securities	316,992	140,518
Capitalized software development costs	(8,626)	(5,351)
Purchases of long-lived assets	(6,319)	(2,653)
Net cash provided by (used in) investing activities	71,645	(130,201)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on finance leases and notes payable	(1,954)	(1,455)
Proceeds from exercises of stock options	8,231	15,328
Value of equity awards withheld for tax liabilities	(1,674)	(1,062)
Net cash provided by financing activities	4,603	12,811
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	91,783	(126,503)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—Beginning of period	253,735	505,334
CASH, CASH EQUIVALENTS AND RESTRICTED CASH —End of period	345,518	378,831
Cash paid for income taxes, net	257	(34)
Cash paid for interest	198	148
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property, equipment and intangible assets, accrued but not paid	5,510	1,821
Purchases of property and equipment through finance leases	0	13,616
Value of common stock issued and stock awards assumed in acquisition	0	2,850,518
Stock-based compensation capitalized in software development costs	$ 3,418	$ 1,623

Organization and Description of Business	3 Months Ended
Organization and Description of Business	Mar. 31, 2020
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, Brazil, Colombia, Czech Republic, Estonia, France, Germany, Hong Kong, India, Ireland, Japan, the Netherlands, Singapore, Spain, Sweden, the United Kingdom and the United States.

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2020
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 the Company's Annual Report on Form 10-K filed with the SEC on March 2, 2020 (“Annual Report”). The condensed consolidated balance sheet as of December 31, 2019, 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, stockholders' equity and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2020 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, 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 sales credit reserves; 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 and accounts receivable. The Company maintains cash, cash equivalents and marketable securities 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 deteriorates substantially, operating results could be adversely affected. To reduce credit risk, management performs 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 months ended March 31, 2020 and 2019, no customer organization accounted for more than 10% of the Company’s total revenue. As of March 31, 2020 and December 31, 2019, 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 months ended March 31, 2020 and 2019, the Company recognized $12.8 million and $10.8 million of revenue, respectively, that was included in the deferred revenue and customer deposits balance as of the end of the prior 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 March 31, 2020 and December 31, 2019 were $36.8 million and $30.4 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 $2.0 million and $0.7 million in the three months ended March 31, 2020 and 2019, respectively, and is included in sales and marketing expenses in the accompanying condensed consolidated statements of operations. (g)Recently Adopted Accounting Guidance In August 2018, the Financial Accounting Standards Board ("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 guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing costs incurred to develop or obtain internal-use software. The guidance is effective for interim and annual periods beginning after December 15, 2019. The Company adopted this guidance effective January 1, 2020. The adoption of this guidance did not have a material impact on the Company's 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. In November 2019, the FASB issued ASU 2019-11, "Codification Improvements to Topic 326, Financial Instruments - Credit Losses", which clarifies the accounting treatment and disclosure requirements for assets purchased with credit deterioration, troubled debt restructurings, and certain other investments. In February 2020, the FASB issued ASU 2020-02, "Financial Instruments—Credit Losses (Topic 326) and Leases (Topic 842) Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 119 and Update to SEC Section on Effective Date Related to Accounting Standards Update No. 2016-02, Leases (Topic 842)." This standard provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. These ASUs are effective for interim and annual periods beginning after December 15, 2019, and the Company adopted them effective January 1, 2020. As of the date of adoption, this guidance did not have a material impact on the Company's consolidated financial statements. (h)Recently Issued Accounting Guidance, Not yet Adopted In December 2019, the FASB issued ASU 2019-12, "Simplifying the Accounting for Income Taxes", which simplifies the accounting for income taxes by removing certain exceptions to the general principles for income taxes. The standard is effective for interim and annual periods beginning after December 15, 2020, with early adoption permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following tables provide the financial assets measured at fair value on a recurring basis:


	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value Hierarchy as of March 31, 2020									Aggregate Fair Value
													Level 1		Level 2		Level 3

Financial Assets:	(In thousands)
Cash and cash equivalents:
Money market funds	$	275,948	$	—	$	—	$	275,948	$	—	$	—	$	275,948


Total included in cash and cash equivalents	275,948		—		—		275,948		—		—		275,948
Marketable securities:
U.S. Treasury securities	193,234		1,927		—		195,161		—		—		195,161
Corporate debt securities and commercial paper	1,311,047		2,556		(10,895)		11,000		1,291,708		—		1,302,708
Total marketable securities	1,504,281		4,483		(10,895)		206,161		1,291,708		—		1,497,869
Strategic investments	5,750		1,944		—		—		—		7,694		7,694
Total financial assets	$	1,785,979	$	6,427	$	(10,895)	$	482,109	$	1,291,708	$	7,694	$	1,781,511


	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value Hierarchy as of December 31, 2019									Aggregate Fair Value
													Level 1		Level 2		Level 3

Financial Assets:	(In thousands)
Cash and cash equivalents:
Money market funds	$	153,252	$	—	$	—	$	153,252	$	—	$	—	$	153,252
Reverse repurchase agreements	35,800		—		—		—		35,800		—		35,800

Total included in cash and cash equivalents	189,052		—		—		153,252		35,800		—		189,052
Marketable securities:
U.S. Treasury securities	215,847		241		(3)		216,085		—		—		216,085
Corporate debt securities and commercial paper	1,378,487		4,516		(55)		5,000		1,377,948		—		1,382,948
Total marketable securities	1,594,334		4,757		(58)		221,085		1,377,948		—		1,599,033
Strategic investments	5,500		—		—		—		—		5,500		5,500
Total financial assets	$	1,788,886	$	4,757	$	(58)	$	374,337	$	1,413,748	$	5,500	$	1,793,585

The Company's primary objective when investing excess cash is preservation of capital, hence the Company's marketable securities consist primarily of US Treasury securities, high credit quality corporate debt securities and commercial paper. As the Company views its marketable securities as available to support its current operations, it has classified all available for sale securities as short-term. As of March 31, 2020 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 March 31, 2020, the Company anticipates that it will recover the entire amortized cost basis of such fixed income securities before maturity.

The Company regularly reviews the changes to the rating of its debt securities by rating agencies as well as reasonably monitors the surrounding economic conditions to assess the risk of expected credit losses. As of March 31, 2020, the risk of expected credit losses was insignificant.

Interest earned on marketable securities was $8.8 million and $1.5 million in the three months ended March 31, 2020 and 2019, 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 March 31, 2020						As of December 31, 2019
	Amortized Cost		Aggregate Fair Value		Amortized Cost		Aggregate Fair Value

Financial Assets:	(In thousands)
Less than one year	$	787,710	$	788,246	$	859,996	$	861,181
One to three years	716,571		709,623		734,338		737,852
Total	$	1,504,281	$	1,497,869	$	1,594,334	$	1,599,033

The Company holds strategic investments with a fair value of $7.7 million in debt and equity securities of privately held companies in which the Company does not have a controlling interest or significant influence. These securities are recorded as other long-term assets in the accompanying condensed consolidated balance sheets. The Company classifies its strategic investments as Level 3 within the fair value hierarchy based on the nature of the fair value inputs and judgment involved in the valuation process.

As of March 31, 2020, and December 31, 2019, the fair value of the 0.25% convertible senior notes due 2023 (the “Notes”), as further described in Note 8 below, was approximately $768.2 million and $841.3 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.

- 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

3 Months Ended

Mar. 31, 2020

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consisted of the following:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Capitalized internal-use software development costs	$	110,918	$	100,155
Data center equipment ⁽¹⁾	22,018		22,009
Leasehold improvements	63,961		55,886
Office equipment	27,001		25,083
Furniture and fixtures ⁽¹⁾	10,253		10,095
Software	9,676		9,176
Total property and equipment	243,827		222,404
Less: accumulated depreciation and amortization	(92,883)		(81,148)
Total property and equipment, net	$	150,944	$	141,256

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

Depreciation and amortization expense was $11.9 million and $7.6 million for the three months ended March 31, 2020 and 2019, respectively.

The Company capitalized $12.0 million and $7.0 million in internal-use software development costs in the three months ended March 31, 2020 and 2019, respectively, of which $3.4 million and $1.6 million, respectively, was stock-based compensation expense. Amortization of capitalized software development costs was $4.6 million and $3.8 million in the three months ended March 31, 2020 and 2019, respectively.

Right-of-Use Asset and Lease Liabilities

3 Months Ended

Mar. 31, 2020

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 sheets.

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 accounts for as a single lease component. When estimating the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain such options will be exercised. 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 March 31, 2020, the Company had 23 leased properties with remaining lease terms from less than one year to slightly over nine years, some of which include options to extend the leases for up to 5.0 years.

The components of the lease expense recorded in the accompanying condensed consolidated statements of operations were as follows:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Operating lease cost	$	10,424	$	7,173
Finance lease cost:
Amortization of assets	1,904		1,163
Interest on lease liabilities	198		148
Short-term lease cost	1,412		1,435
Variable lease cost	1,296		487
Total net lease cost	$	15,234	$	10,406

Supplemental balance sheet information related to leases was as follows:


		As of		As of
		March 31,		December 31,
Leases	Classification	2020		2019

Assets:		(In thousands)
Operating lease assets	Operating right-of-use asset, net of accumulated amortization ⁽¹⁾	$	159,439	$	156,741
Finance lease assets	Property and equipment, net of accumulated depreciation ⁽²⁾	12,866		14,770
Total leased assets		$	172,305	$	171,511

Liabilities:
Current
Operating	Operating lease liability, current	$	29,949	$	27,156
Finance	Financing lease liability, current	6,539		6,924
Noncurrent
Operating	Operating lease liability, noncurrent	140,120		139,200
Finance	Finance lease liability, noncurrent	7,250		8,746
Total lease liabilities		$	183,858	$	182,026

____________________

⁽¹⁾ Operating lease assets are recorded net of accumulated amortization of $31.2 million and $23.2 million as of March 31, 2020 and December 31, 2019, respectively.

⁽²⁾ Finance lease assets are recorded net of accumulated depreciation of $7.9 million and $6.0 million as of March 31, 2020 and December 31, 2019, respectively.

Supplemental cash flow and other information related to leases was as follows:


	Three Months Ended March 31,
	2020			2019

Cash paid for amounts included in the measurement of lease liabilities:	(In thousands)
Operating cash flows from operating leases	$	9,953		$	3,994
Operating cash flows from finance leases (interest)	$	198		$	148
Financing cash flows from finance leases	$	1,881		$	961

Weighted average remaining lease term (in years):
Operating leases	5.8			7.1
Finance leases	2.9			3.3

Weighted average discount rate:
Operating leases	5.7		%	5.8		%
Finance leases	5.3		%	5.2		%

Maturities of lease liabilities were as follows:


	As of March 31, 2020
	Operating Leases		Finance Leases

Year ended December 31,	(In thousands)
2020 (remaining nine months)	$	29,148	$	5,507
2021	38,190		4,659
2022	37,145		2,333
2023	29,378		1,581
2024	25,549		315
Thereafter	43,126		581
Total lease payments	202,536		14,976
Less: imputed interest	(32,467)		(1,187)
Total lease obligations	170,069		13,789
Less: current obligations	(29,949)		(6,539)
Long-term lease obligations	$	140,120	$	7,250

As of March 31, 2020, the Company had an additional operating lease obligation totaling $43.5 million related to a lease that will commence in the second quarter of 2020 with a lease term of 6.8 years. The Company had an additional finance lease obligation of $0.7 million related to a lease that will commence in the second quarter of 2020 with a lease term of 6.8 years.

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 sheets.

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 accounts for as a single lease component. When estimating the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain such options will be exercised. 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 March 31, 2020, the Company had 23 leased properties with remaining lease terms from less than one year to slightly over nine years, some of which include options to extend the leases for up to 5.0 years.

The components of the lease expense recorded in the accompanying condensed consolidated statements of operations were as follows:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Operating lease cost	$	10,424	$	7,173
Finance lease cost:
Amortization of assets	1,904		1,163
Interest on lease liabilities	198		148
Short-term lease cost	1,412		1,435
Variable lease cost	1,296		487
Total net lease cost	$	15,234	$	10,406

Supplemental balance sheet information related to leases was as follows:


		As of		As of
		March 31,		December 31,
Leases	Classification	2020		2019

Assets:		(In thousands)
Operating lease assets	Operating right-of-use asset, net of accumulated amortization ⁽¹⁾	$	159,439	$	156,741
Finance lease assets	Property and equipment, net of accumulated depreciation ⁽²⁾	12,866		14,770
Total leased assets		$	172,305	$	171,511

Liabilities:
Current
Operating	Operating lease liability, current	$	29,949	$	27,156
Finance	Financing lease liability, current	6,539		6,924
Noncurrent
Operating	Operating lease liability, noncurrent	140,120		139,200
Finance	Finance lease liability, noncurrent	7,250		8,746
Total lease liabilities		$	183,858	$	182,026

____________________

⁽¹⁾ Operating lease assets are recorded net of accumulated amortization of $31.2 million and $23.2 million as of March 31, 2020 and December 31, 2019, respectively.

⁽²⁾ Finance lease assets are recorded net of accumulated depreciation of $7.9 million and $6.0 million as of March 31, 2020 and December 31, 2019, respectively.

Supplemental cash flow and other information related to leases was as follows:


	Three Months Ended March 31,
	2020			2019

Cash paid for amounts included in the measurement of lease liabilities:	(In thousands)
Operating cash flows from operating leases	$	9,953		$	3,994
Operating cash flows from finance leases (interest)	$	198		$	148
Financing cash flows from finance leases	$	1,881		$	961

Weighted average remaining lease term (in years):
Operating leases	5.8			7.1
Finance leases	2.9			3.3

Weighted average discount rate:
Operating leases	5.7		%	5.8		%
Finance leases	5.3		%	5.2		%

Maturities of lease liabilities were as follows:


	As of March 31, 2020
	Operating Leases		Finance Leases

Year ended December 31,	(In thousands)
2020 (remaining nine months)	$	29,148	$	5,507
2021	38,190		4,659
2022	37,145		2,333
2023	29,378		1,581
2024	25,549		315
Thereafter	43,126		581
Total lease payments	202,536		14,976
Less: imputed interest	(32,467)		(1,187)
Total lease obligations	170,069		13,789
Less: current obligations	(29,949)		(6,539)
Long-term lease obligations	$	140,120	$	7,250

As of March 31, 2020, the Company had an additional operating lease obligation totaling $43.5 million related to a lease that will commence in the second quarter of 2020 with a lease term of 6.8 years. The Company had an additional finance lease obligation of $0.7 million related to a lease that will commence in the second quarter of 2020 with a lease term of 6.8 years.

Goodwill and Intangible Assets

3 Months Ended

Mar. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

Goodwill

Changes in Goodwill balance were as follows:


	Total
	(In thousands)
Balance as of December 31, 2019	$	2,296,784
Measurement period adjustments	(5,147)
Balance as of March 31, 2020	$	2,291,637

Intangible assets

Intangible assets consisted of the following:


	As of March 31, 2020
	Gross		Accumulated Amortization		Net

Amortizable intangible assets:	(In thousands)
Developed technology	$	334,599	$	(67,259)	$	267,340
Customer relationships	185,594		(33,296)		152,298
Supplier relationships	4,356		(2,006)		2,350
Trade names	20,060		(4,727)		15,333
Patent	2,905		(288)		2,617
Total amortizable intangible assets	547,514		(107,576)		439,938
Non-amortizable intangible assets:
Telecommunication licenses	4,920		—		4,920
Domain names	32		—		32
Trademarks and other	263		—		263
Total	$	552,729	$	(107,576)	$	445,153


	As of December 31, 2019
	Gross		Accumulated Amortization		Net

Amortizable intangible assets:	(In thousands)
Developed technology	$	333,980	$	(55,390)	$	278,590
Customer relationships	182,339		(26,347)		155,992
Supplier relationships	4,356		(1,532)		2,824
Trade name	20,060		(3,727)		16,333
Patent	2,707		(262)		2,445
Total amortizable intangible assets	543,442		(87,258)		456,184
Non-amortizable intangible assets:
Telecommunication licenses	4,370		—		4,370
Domain names	32		—		32
Trademarks and other	263		—		263
Total	$	548,107	$	(87,258)	$	460,849

Amortization expense was $20.3 million and $13.6 million for the three months ended March 31, 2020 and 2019, respectively.

Total estimated future amortization expense is as follows:


	As of
	March 31,
	2020

Year Ended December 31,	(In thousands)
2020 (remaining nine months)	$	60,796
2021	80,480
2022	77,865
2023	74,583
2024	69,304
Thereafter	76,910
Total	$	439,938

Accrued Expenses and Other Liabilities

3 Months Ended

Mar. 31, 2020

Accrued Liabilities and Other Liabilities [Abstract]

Accrued Expenses and Other Liabilities

Accrued expenses and other current liabilities consisted of the following:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Accrued payroll and related	$	30,198	$	20,462
Accrued bonus and commission	11,052		12,898
Accrued cost of revenue	71,479		47,563
Sales and other taxes payable	29,758		28,592
ESPP contributions	11,521		4,023


VAT and other taxes	4,152		4,838
Acquisition holdback	4,520		6,520
Accrued other expense	32,713		22,785
Total accrued expenses and other current liabilities	$	195,393	$	147,681

Other long-term liabilities consisted of the following:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)

Deferred tax liability	$	8,362	$	7,535
Acquisition holdback	3,750		3,750


Accrued other expenses	8,854		6,462
Total other long-term liabilities	$	20,966	$	17,747

Notes Payable

3 Months Ended

Mar. 31, 2020

Long-term Debt, Unclassified [Abstract]

Notes Payable

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 by us were $537.0 million.

Each $1,000 principal amount of the Notes is initially convertible into 14.104 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 March 31, 2020, 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 March 31, 2020 (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 April 1, 2020 through June 30, 2020. 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 continues to classify the Notes as a long-term liability in its condensed consolidated balance sheet as of March 31, 2020, based on contractual settlement provisions. 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:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Principal	$	549,998	$	549,999
Unamortized discount	(78,953)		(84,647)
Unamortized issuance costs	(6,678)		(7,162)
Net carrying amount	$	464,367	$	458,190

The net carrying amount of the equity component of the Notes was as follows:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Proceeds allocated to the conversion options (debt discount)	$	119,434	$	119,435
Issuance costs	(2,819)		(2,819)
Net carrying amount	$	116,615	$	116,616

The following table sets forth the interest expense recognized related to the Notes:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Contractual interest expense	$	344	$	344
Amortization of debt issuance costs	484		458
Amortization of debt discount	5,694		5,383
Total interest expense related to the Notes	$	6,522	$	6,185

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 7,757,158 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.

Supplemental Balance Sheet Information

3 Months Ended

Mar. 31, 2020

Receivables [Abstract]

Supplemental Balance Sheet Information

A roll-forward of the Company’s reserves is as follows:

(a)Allowance for doubtful accounts:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Balance, beginning of period	$	6,287	$	4,945
Additions	4,261		(245)

Write-offs	(1,463)		(419)
Balance, end of period	$	9,085	$	4,281


Percentage of revenue						2		%				2		%

(b)Sales credit reserve:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Balance, beginning of period	$	6,784	$	3,015
Additions	8,174		2,681

Deductions against reserve	(5,271)		(2,865)
Balance, end of period	$	9,687	$	2,831


Percentage of revenue						3		%				1		%

Revenue by Geographic Area

3 Months Ended

Mar. 31, 2020

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:


	Three Months Ended March 31,
	2020		2019

Revenue by geographic area:	(In thousands)
United States	$	261,813	$	166,553
International	103,055		66,586
Total	$	364,868	$	233,139


Percentage of revenue by geographic area:
United States	72	%	71	%
International	28	%	29	%

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

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and ContingenciesLease and Other Commitments The Company entered into various non-cancelable operating lease agreements for its facilities with remaining lease terms from less than one year to slightly over nine 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 months ended March 31, 2020, the Company entered into several non-cancelable vendor agreements with terms up to two years for a total purchase commitment of $16.8 million. 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 the Company 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. On January 9, 2020, the Federal Circuit Court affirmed the district court’s judgment. Telesign has not indicated whether it will seek a further appeal of the judgment. Based on, among other things, the district court’s judgment being affirmed on appeal in the Company’s favor, the Company does not believe a loss is probable 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 U.S. Patent and Trademark Office (“U.S. 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. 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 the Company, its partners and its customers by determining the scope, enforceability and validity of third-party proprietary rights, or to establish our 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. 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 March 31, 2020 and December 31, 2019, no amounts were accrued. ther 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, 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 had nexus, and the sourcing of revenues to those jurisdictions. Starting in March 2017, the Company began collecting these taxes from customers in various jurisdiction and since then has expanded to most jurisdictions where these taxes are now being collected. Simultaneously, the Company continues to be in discussions with certain jurisdictions regarding its prior sales and other taxes, if any, that the Company may owe. As of March 31, 2020 and December 31, 2019, the liability recorded for these taxes was $27.5 million and $27.0 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

3 Months Ended

Mar. 31, 2020

Stockholders' Equity Note [Abstract]

Stockholders' Equity

Stockholders’ Equity

Preferred Stock

As of March 31, 2020 and December 31, 2019, the Company had authorized 100,000,000 shares of preferred stock, par value $0.001, of which no shares were issued and outstanding.

Common Stock

As of March 31, 2020 and December 31, 2019, 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 March 31, 2020, 128,606,443 shares of Class A common stock and 11,356,940 shares of Class B common stock were issued and outstanding. As of December 31, 2019, 126,882,172 shares of Class A common stock and 11,530,627 shares of Class B common stock were issued and outstanding.

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


	As of	As of
	March 31,	December 31,
	2020	2019

Stock options issued and outstanding	7,492,970	7,705,848
Nonvested restricted stock units issued and outstanding	8,039,823	8,490,517
Class A common stock reserved for Twilio.org	773,571	795,673
Stock-based awards available for grant under 2016 Plan	20,998,004	14,957,734
Stock-based awards available for grant under 2016 ESPP	5,233,081	3,848,953
Class A common stock reserved for the convertible senior notes	10,472,165	10,472,165
Total	53,009,614	46,270,890

Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

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, 2020 and 2019, the shares available for grant under the 2016 Plan were automatically increased by 6,920,640 and 5,004,011 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, Inc. ("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”), as amended, initially 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 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, 2020 and 2019, the shares available for grant under the 2016 ESPP were automatically increased by 1,384,128 and 1,000,802 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. The 2016 ESPP provides for separate six-month offering periods beginning in May and November of each fiscal year.

On each purchase date, eligible employees 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. As of March 31, 2020, total unrecognized compensation cost related to the 2016 ESPP was $1.3 million, which will be amortized over a weighted-average period of 0.1 years.

Stock Options

Stock option activity under the Company's 2008 Plan and 2016 Plan as well as respective Stock Incentive Plans assumed in the SendGrid acquisition was as follows:


	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, 2019	7,150,848	$	28.79	6.47	$	511,971
Granted	534,412	121.20

Exercised	(669,030)	12.30
Forfeited and canceled	(78,260)	52.44
Outstanding options as of March 31, 2020	6,937,970	$	37.23	7.16	$	400,612
Options vested and exercisable as of March 31, 2020	4,545,317	$	18.07	6.39	$	329,352


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Aggregate intrinsic value of stock options exercised ⁽¹⁾	$	68,359	$	187,016
Total estimated grant date fair value of options vested	$	23,335	$	55,310
Weighted-average grant date fair value per share of options granted	$	60.47	$	58.00
____________________
⁽¹⁾ 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.

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. All performance conditions have been met. The stock options are amortized over a derived service period, as adjusted, of 3.1 years, 3.9 years and 4.4 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, 2019	555,000	$	31.72	4.16	$	36,941
Granted	—	—

Exercised	—	—
Forfeited and canceled	—	—
Outstanding options as of March 31, 2020	555,000	$	31.72	3.91	$	32,062
Options vested and exercisable as of March 31, 2020	462,499	$	31.72	3.91	$	26,719

As of March 31, 2020, total unrecognized compensation cost related to nonvested stock options was $109.1 million, which will be amortized on a ratable basis over a weighted-average period of 2.1 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, 2019	8,490,517	$	74.21	$	830,167
Granted	728,343	117.09

Vested	(872,870)	62.65
Forfeited and canceled	(306,167)	$	75.56
Nonvested RSUs as of March 31, 2020	8,039,823	$	80.61	$	713,474

As of March 31, 2020, total unrecognized compensation cost related to nonvested RSUs was $579.9 million, which will be amortized over a weighted-average period of 2.6 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 March 31,
Employee Stock Options:	2020	2019

Fair value of common stock	$117.9 - $126.7	$111.3 - $130.7
Expected term (in years)	6.08	0.33 - 6.08
Expected volatility	51.9%	48.3% - 66.5%
Risk-free interest rate	1.3% - 1.4%	2.4% - 2.5%
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						$31.7

Stock-Based Compensation Expense

The Company recorded the total stock-based compensation expense as follows:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Cost of revenue	$	1,837	$	1,809
Research and development	33,209		25,339
Sales and marketing	19,943		11,749
General and administrative	14,036		19,427
Total	$	69,025	$	58,324

Net Loss Per Share Attributable to Common Stockholders

3 Months Ended

Mar. 31, 2020

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:


	Three Months Ended March 31,
	2020		2019

Net loss attributable to common stockholders (in thousands)	$	(94,791)	$	(36,503)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	139,231,594		116,590,513
Net loss per share attributable to common stockholders, basic and diluted	$	(0.68)	$	(0.31)

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 March 31,
	2020	2019

Stock options issued and outstanding	7,492,970	10,045,155
Nonvested restricted stock units issued and outstanding	8,039,823	8,813,737
Class A common stock reserved for Twilio.org	773,571	776,334
Class A common stock committed under 2016 ESPP	212,028	113,959
Conversion spread ⁽¹⁾	2,747,996	2,873,836
Unvested shares subject to repurchase	—	1,250
Total	19,266,388	22,624,271

____________________
⁽¹⁾ 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	3 Months Ended
Income Taxes	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company recorded an income tax provision of $1.0 million and income tax benefit of $51.7 million for the three months ended March 31, 2020 and 2019, respectively. 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 months ended March 31, 2020, 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. The tax benefit for the three months ended March 31, 2019, was primarily related to a partial release of valuation allowance, of which $49.2 million was directly related to the day one impact from the acquisition of SendGrid. 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. As a result, during the three months ended March 31, 2019, the Company released a total of $51.6 million of its U.S. valuation allowance. On March 27, 2020, the Coronavirus Aid, Relief and Economic Security (CARES) Act was enacted and signed into U.S. law to provide economic relief to individuals and businesses facing economic hardship as a result of the COVID-19 pandemic. Changes in tax laws or rates are accounted for in the period of enactment. The income tax provisions of the CARES Act do not have a significant impact on our current taxes, deferred taxes, and uncertain tax positions of the Company.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2020
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 the Company's Annual Report on Form 10-K filed with the SEC on March 2, 2020 (“Annual Report”). The condensed consolidated balance sheet as of December 31, 2019, 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, stockholders' equity and cash flows for the interim periods, but are not necessarily indicative of the results of operations to be anticipated for the full year 2020 or any future period.
Principles of Consolidation	Principles of ConsolidationThe 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 EstimatesThe 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, 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 sales credit reserves; 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 RiskFinancial instruments that potentially expose the Company to a concentration of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains cash, cash equivalents and marketable securities 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 deteriorates substantially, operating results could be adversely affected. To reduce credit risk, management performs 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 months ended March 31, 2020 and 2019, the Company recognized $12.8 million and $10.8 million of revenue, respectively, that was included in the deferred revenue and customer deposits balance as of the end of the prior 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 Issued Accounting Guidance	Recently Adopted Accounting Guidance In August 2018, the Financial Accounting Standards Board ("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 guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing costs incurred to develop or obtain internal-use software. The guidance is effective for interim and annual periods beginning after December 15, 2019. The Company adopted this guidance effective January 1, 2020. The adoption of this guidance did not have a material impact on the Company's 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. In November 2019, the FASB issued ASU 2019-11, "Codification Improvements to Topic 326, Financial Instruments - Credit Losses", which clarifies the accounting treatment and disclosure requirements for assets purchased with credit deterioration, troubled debt restructurings, and certain other investments. In February 2020, the FASB issued ASU 2020-02, "Financial Instruments—Credit Losses (Topic 326) and Leases (Topic 842) Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 119 and Update to SEC Section on Effective Date Related to Accounting Standards Update No. 2016-02, Leases (Topic 842)." This standard provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. These ASUs are effective for interim and annual periods beginning after December 15, 2019, and the Company adopted them effective January 1, 2020. As of the date of adoption, this guidance did not have a material impact on the Company's consolidated financial statements. (h)Recently Issued Accounting Guidance, Not yet Adopted In December 2019, the FASB issued ASU 2019-12, "Simplifying the Accounting for Income Taxes", which simplifies the accounting for income taxes by removing certain exceptions to the general principles for income taxes. The standard is effective for interim and annual periods beginning after December 15, 2020, with early adoption permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

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:


	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value Hierarchy as of March 31, 2020									Aggregate Fair Value
													Level 1		Level 2		Level 3

Financial Assets:	(In thousands)
Cash and cash equivalents:
Money market funds	$	275,948	$	—	$	—	$	275,948	$	—	$	—	$	275,948


Total included in cash and cash equivalents	275,948		—		—		275,948		—		—		275,948
Marketable securities:
U.S. Treasury securities	193,234		1,927		—		195,161		—		—		195,161
Corporate debt securities and commercial paper	1,311,047		2,556		(10,895)		11,000		1,291,708		—		1,302,708
Total marketable securities	1,504,281		4,483		(10,895)		206,161		1,291,708		—		1,497,869
Strategic investments	5,750		1,944		—		—		—		7,694		7,694
Total financial assets	$	1,785,979	$	6,427	$	(10,895)	$	482,109	$	1,291,708	$	7,694	$	1,781,511


	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value Hierarchy as of December 31, 2019									Aggregate Fair Value
													Level 1		Level 2		Level 3

Financial Assets:	(In thousands)
Cash and cash equivalents:
Money market funds	$	153,252	$	—	$	—	$	153,252	$	—	$	—	$	153,252
Reverse repurchase agreements	35,800		—		—		—		35,800		—		35,800

Total included in cash and cash equivalents	189,052		—		—		153,252		35,800		—		189,052
Marketable securities:
U.S. Treasury securities	215,847		241		(3)		216,085		—		—		216,085
Corporate debt securities and commercial paper	1,378,487		4,516		(55)		5,000		1,377,948		—		1,382,948
Total marketable securities	1,594,334		4,757		(58)		221,085		1,377,948		—		1,599,033
Strategic investments	5,500		—		—		—		—		5,500		5,500
Total financial assets	$	1,788,886	$	4,757	$	(58)	$	374,337	$	1,413,748	$	5,500	$	1,793,585

Schedule of contractual maturities of marketable securities

The following table summarizes the contractual maturities of marketable securities:


	As of March 31, 2020						As of December 31, 2019
	Amortized Cost		Aggregate Fair Value		Amortized Cost		Aggregate Fair Value

Financial Assets:	(In thousands)
Less than one year	$	787,710	$	788,246	$	859,996	$	861,181
One to three years	716,571		709,623		734,338		737,852
Total	$	1,504,281	$	1,497,869	$	1,594,334	$	1,599,033

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2020

Property, Plant and Equipment [Abstract]

Schedule of property and equipment

Property and equipment consisted of the following:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Capitalized internal-use software development costs	$	110,918	$	100,155
Data center equipment ⁽¹⁾	22,018		22,009
Leasehold improvements	63,961		55,886
Office equipment	27,001		25,083
Furniture and fixtures ⁽¹⁾	10,253		10,095
Software	9,676		9,176
Total property and equipment	243,827		222,404
Less: accumulated depreciation and amortization	(92,883)		(81,148)
Total property and equipment, net	$	150,944	$	141,256

____________________
⁽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)

3 Months Ended

Mar. 31, 2020

Leases [Abstract]

Lease, Cost

The components of the lease expense recorded in the accompanying condensed consolidated statements of operations were as follows:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Operating lease cost	$	10,424	$	7,173
Finance lease cost:
Amortization of assets	1,904		1,163
Interest on lease liabilities	198		148
Short-term lease cost	1,412		1,435
Variable lease cost	1,296		487
Total net lease cost	$	15,234	$	10,406

Supplemental cash flow and other information related to leases was as follows:


	Three Months Ended March 31,
	2020			2019

Cash paid for amounts included in the measurement of lease liabilities:	(In thousands)
Operating cash flows from operating leases	$	9,953		$	3,994
Operating cash flows from finance leases (interest)	$	198		$	148
Financing cash flows from finance leases	$	1,881		$	961

Weighted average remaining lease term (in years):
Operating leases	5.8			7.1
Finance leases	2.9			3.3

Weighted average discount rate:
Operating leases	5.7		%	5.8		%
Finance leases	5.3		%	5.2		%

Assets and Liabilities, Lessee

Supplemental balance sheet information related to leases was as follows:


		As of		As of
		March 31,		December 31,
Leases	Classification	2020		2019

Assets:		(In thousands)
Operating lease assets	Operating right-of-use asset, net of accumulated amortization ⁽¹⁾	$	159,439	$	156,741
Finance lease assets	Property and equipment, net of accumulated depreciation ⁽²⁾	12,866		14,770
Total leased assets		$	172,305	$	171,511

Liabilities:
Current
Operating	Operating lease liability, current	$	29,949	$	27,156
Finance	Financing lease liability, current	6,539		6,924
Noncurrent
Operating	Operating lease liability, noncurrent	140,120		139,200
Finance	Finance lease liability, noncurrent	7,250		8,746
Total lease liabilities		$	183,858	$	182,026

____________________

⁽¹⁾ Operating lease assets are recorded net of accumulated amortization of $31.2 million and $23.2 million as of March 31, 2020 and December 31, 2019, respectively.

⁽²⁾ Finance lease assets are recorded net of accumulated depreciation of $7.9 million and $6.0 million as of March 31, 2020 and December 31, 2019, respectively.

Lessee, Operating Lease, Liability, Maturity

Maturities of lease liabilities were as follows:


	As of March 31, 2020
	Operating Leases		Finance Leases

Year ended December 31,	(In thousands)
2020 (remaining nine months)	$	29,148	$	5,507
2021	38,190		4,659
2022	37,145		2,333
2023	29,378		1,581
2024	25,549		315
Thereafter	43,126		581
Total lease payments	202,536		14,976
Less: imputed interest	(32,467)		(1,187)
Total lease obligations	170,069		13,789
Less: current obligations	(29,949)		(6,539)
Long-term lease obligations	$	140,120	$	7,250

Finance Lease, Liability, Maturity

Maturities of lease liabilities were as follows:


	As of March 31, 2020
	Operating Leases		Finance Leases

Year ended December 31,	(In thousands)
2020 (remaining nine months)	$	29,148	$	5,507
2021	38,190		4,659
2022	37,145		2,333
2023	29,378		1,581
2024	25,549		315
Thereafter	43,126		581
Total lease payments	202,536		14,976
Less: imputed interest	(32,467)		(1,187)
Total lease obligations	170,069		13,789
Less: current obligations	(29,949)		(6,539)
Long-term lease obligations	$	140,120	$	7,250

Goodwill and Intangible Assets (Tables)

3 Months Ended

Mar. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of goodwill balance

oodwill balance were as follows:


	Total
	(In thousands)
Balance as of December 31, 2019	$	2,296,784
Measurement period adjustments	(5,147)
Balance as of March 31, 2020	$	2,291,637

Schedule of intangible assets

Intangible assets consisted of the following:


	As of March 31, 2020
	Gross		Accumulated Amortization		Net

Amortizable intangible assets:	(In thousands)
Developed technology	$	334,599	$	(67,259)	$	267,340
Customer relationships	185,594		(33,296)		152,298
Supplier relationships	4,356		(2,006)		2,350
Trade names	20,060		(4,727)		15,333
Patent	2,905		(288)		2,617
Total amortizable intangible assets	547,514		(107,576)		439,938
Non-amortizable intangible assets:
Telecommunication licenses	4,920		—		4,920
Domain names	32		—		32
Trademarks and other	263		—		263
Total	$	552,729	$	(107,576)	$	445,153


	As of December 31, 2019
	Gross		Accumulated Amortization		Net

Amortizable intangible assets:	(In thousands)
Developed technology	$	333,980	$	(55,390)	$	278,590
Customer relationships	182,339		(26,347)		155,992
Supplier relationships	4,356		(1,532)		2,824
Trade name	20,060		(3,727)		16,333
Patent	2,707		(262)		2,445
Total amortizable intangible assets	543,442		(87,258)		456,184
Non-amortizable intangible assets:
Telecommunication licenses	4,370		—		4,370
Domain names	32		—		32
Trademarks and other	263		—		263
Total	$	548,107	$	(87,258)	$	460,849

Schedule of total estimated future amortization expense

Total estimated future amortization expense is as follows:


	As of
	March 31,
	2020

Year Ended December 31,	(In thousands)
2020 (remaining nine months)	$	60,796
2021	80,480
2022	77,865
2023	74,583
2024	69,304
Thereafter	76,910
Total	$	439,938

Accrued Expenses and Other Liabilities (Tables)

3 Months Ended

Mar. 31, 2020

Accrued Liabilities and Other Liabilities [Abstract]

Schedule of accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Accrued payroll and related	$	30,198	$	20,462
Accrued bonus and commission	11,052		12,898
Accrued cost of revenue	71,479		47,563
Sales and other taxes payable	29,758		28,592
ESPP contributions	11,521		4,023


VAT and other taxes	4,152		4,838
Acquisition holdback	4,520		6,520
Accrued other expense	32,713		22,785
Total accrued expenses and other current liabilities	$	195,393	$	147,681

Schedule of other long-term liabilities

Other long-term liabilities consisted of the following:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)

Deferred tax liability	$	8,362	$	7,535
Acquisition holdback	3,750		3,750


Accrued other expenses	8,854		6,462
Total other long-term liabilities	$	20,966	$	17,747

Notes Payable (Tables)

3 Months Ended

Mar. 31, 2020

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:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Principal	$	549,998	$	549,999
Unamortized discount	(78,953)		(84,647)
Unamortized issuance costs	(6,678)		(7,162)
Net carrying amount	$	464,367	$	458,190

The net carrying amount of the equity component of the Notes was as follows:


	As of		As of
	March 31,		December 31,
	2020		2019

	(In thousands)
Proceeds allocated to the conversion options (debt discount)	$	119,434	$	119,435
Issuance costs	(2,819)		(2,819)
Net carrying amount	$	116,615	$	116,616

Schedule of interest expense recognized related to the Notes

The following table sets forth the interest expense recognized related to the Notes:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Contractual interest expense	$	344	$	344
Amortization of debt issuance costs	484		458
Amortization of debt discount	5,694		5,383
Total interest expense related to the Notes	$	6,522	$	6,185

Supplemental Balance Sheet Information (Tables)

3 Months Ended

Mar. 31, 2020

Receivables [Abstract]

Schedule of the allowance for doubtful accounts

Allowance for doubtful accounts:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Balance, beginning of period	$	6,287	$	4,945
Additions	4,261		(245)

Write-offs	(1,463)		(419)
Balance, end of period	$	9,085	$	4,281


Percentage of revenue						2		%				2		%

Schedule of the sales credit reserve

Sales credit reserve:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Balance, beginning of period	$	6,784	$	3,015
Additions	8,174		2,681

Deductions against reserve	(5,271)		(2,865)
Balance, end of period	$	9,687	$	2,831


Percentage of revenue						3		%				1		%

Revenue by Geographic Area (Tables)

3 Months Ended

Mar. 31, 2020

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:


	Three Months Ended March 31,
	2020		2019

Revenue by geographic area:	(In thousands)
United States	$	261,813	$	166,553
International	103,055		66,586
Total	$	364,868	$	233,139


Percentage of revenue by geographic area:
United States	72	%	71	%
International	28	%	29	%

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

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	As of
	March 31,	December 31,
	2020	2019

Stock options issued and outstanding	7,492,970	7,705,848
Nonvested restricted stock units issued and outstanding	8,039,823	8,490,517
Class A common stock reserved for Twilio.org	773,571	795,673
Stock-based awards available for grant under 2016 Plan	20,998,004	14,957,734
Stock-based awards available for grant under 2016 ESPP	5,233,081	3,848,953
Class A common stock reserved for the convertible senior notes	10,472,165	10,472,165
Total	53,009,614	46,270,890

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Stock-Based Compensation

Schedule of weighted average grant date fair value


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Aggregate intrinsic value of stock options exercised ⁽¹⁾	$	68,359	$	187,016
Total estimated grant date fair value of options vested	$	23,335	$	55,310
Weighted-average grant date fair value per share of options granted	$	60.47	$	58.00
____________________
⁽¹⁾ 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.

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, 2019	8,490,517	$	74.21	$	830,167
Granted	728,343	117.09

Vested	(872,870)	62.65
Forfeited and canceled	(306,167)	$	75.56
Nonvested RSUs as of March 31, 2020	8,039,823	$	80.61	$	713,474

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						$31.7

Schedule of stock based compensation expense

The Company recorded the total stock-based compensation expense as follows:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Cost of revenue	$	1,837	$	1,809
Research and development	33,209		25,339
Sales and marketing	19,943		11,749
General and administrative	14,036		19,427
Total	$	69,025	$	58,324

Employee and nonemployee stock options

Stock-Based Compensation

Schedule of stock options activity


	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, 2019	7,150,848	$	28.79	6.47	$	511,971
Granted	534,412	121.20

Exercised	(669,030)	12.30
Forfeited and canceled	(78,260)	52.44
Outstanding options as of March 31, 2020	6,937,970	$	37.23	7.16	$	400,612
Options vested and exercisable as of March 31, 2020	4,545,317	$	18.07	6.39	$	329,352

Performance-based stock options

Stock-Based Compensation

Schedule of stock options activity

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. All performance conditions have been met. The stock options are amortized over a derived service period, as adjusted, of 3.1 years, 3.9 years and 4.4 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, 2019	555,000	$	31.72	4.16	$	36,941
Granted	—	—

Exercised	—	—
Forfeited and canceled	—	—
Outstanding options as of March 31, 2020	555,000	$	31.72	3.91	$	32,062
Options vested and exercisable as of March 31, 2020	462,499	$	31.72	3.91	$	26,719

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 March 31,
Employee Stock Options:	2020	2019

Fair value of common stock	$117.9 - $126.7	$111.3 - $130.7
Expected term (in years)	6.08	0.33 - 6.08
Expected volatility	51.9%	48.3% - 66.5%
Risk-free interest rate	1.3% - 1.4%	2.4% - 2.5%
Dividend rate	—%	—%

Net Loss Per Share Attributable to Common Stockholders (Tables)

3 Months Ended

Mar. 31, 2020

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:


	Three Months Ended March 31,
	2020		2019

Net loss attributable to common stockholders (in thousands)	$	(94,791)	$	(36,503)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	139,231,594		116,590,513
Net loss per share attributable to common stockholders, basic and diluted	$	(0.68)	$	(0.31)

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 March 31,
	2020	2019

Stock options issued and outstanding	7,492,970	10,045,155
Nonvested restricted stock units issued and outstanding	8,039,823	8,813,737
Class A common stock reserved for Twilio.org	773,571	776,334
Class A common stock committed under 2016 ESPP	212,028	113,959
Conversion spread ⁽¹⁾	2,747,996	2,873,836
Unvested shares subject to repurchase	—	1,250
Total	19,266,388	22,624,271

____________________
⁽¹⁾ 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 (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Deferred Sales Commissions
Revenue recognized out of adjusted deferred revenue balance	$ 12.8	$ 10.8
Total net capitalized costs	36.8		$ 30.4
Amortization of capitalized costs of obtaining a contract	$ 2.0	$ 0.7
Incremental commission costs of obtaining new contracts
Deferred Sales Commissions
Amortization period for deferred incremental commission costs of obtaining new contracts	5 years

Fair Value Measurements - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Measurements, Financial Assets
Cash and cash equivalents	$ 275,948	$ 189,052
Total amortized cost	1,504,281	1,594,334
Marketable securities, accumulated gross unrealized gain, before tax	4,483	4,757
Marketable securities, gross unrealized losses less than 12 months	(10,895)	(58)
Marketable securities, aggregate fair value	1,497,869	1,599,033
Strategic investments, amortized cost	5,750	5,500
Strategic investments, gross unrealized gains	1,944
Strategic investments	7,694	5,500
Total financial assets, amortized cost or carrying value	1,785,979	1,788,886
Total gross unrealized gains	6,427	4,757
Total financial assets	1,781,511	1,793,585
Note receivable	7,700
U.S. Treasury securities
Fair Value Measurements, Financial Assets
Total amortized cost	193,234	215,847
Marketable securities, accumulated gross unrealized gain, before tax	1,927	241
Marketable securities, gross unrealized losses less than 12 months	0	(3)
Marketable securities, aggregate fair value	195,161	216,085
Corporate debt securities and commercial paper
Fair Value Measurements, Financial Assets
Total amortized cost	1,311,047	1,378,487
Marketable securities, accumulated gross unrealized gain, before tax	2,556	4,516
Marketable securities, gross unrealized losses less than 12 months	(10,895)	(55)
Marketable securities, aggregate fair value	1,302,708	1,382,948
Level 1
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,948	153,252
Marketable securities, aggregate fair value	206,161	221,085
Total financial assets	482,109	374,337
Level 1 \| U.S. Treasury securities
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	195,161	216,085
Level 1 \| Corporate debt securities and commercial paper
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	11,000	5,000
Level 2
Fair Value Measurements, Financial Assets
Cash and cash equivalents	0	35,800
Marketable securities, aggregate fair value	1,291,708	1,377,948
Total financial assets	1,291,708	1,413,748
Level 2 \| U.S. Treasury securities
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	0	0
Level 2 \| Corporate debt securities and commercial paper
Fair Value Measurements, Financial Assets
Marketable securities, aggregate fair value	1,291,708	1,377,948
Level 3
Fair Value Measurements, Financial Assets
Strategic investments	7,694	5,500
Total financial assets	7,694	5,500
Carrying Value \| Money market funds
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,948	153,252
Carrying Value \| Reverse repurchase agreements
Fair Value Measurements, Financial Assets
Cash and cash equivalents		35,800
Aggregate Fair Value \| Money market funds
Fair Value Measurements, Financial Assets
Cash and cash equivalents	275,948	153,252
Aggregate Fair Value \| Reverse repurchase agreements
Fair Value Measurements, Financial Assets
Cash and cash equivalents		35,800
Aggregate Fair Value \| Level 1 \| Money market funds
Fair Value Measurements, Financial Assets
Cash and cash equivalents	$ 275,948	153,252
Aggregate Fair Value \| Level 2 \| Reverse repurchase agreements
Fair Value Measurements, Financial Assets
Cash and cash equivalents		$ 35,800

Fair Value Measurements - Marketable Securities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019
Marketable Securities
Other-than-temporary impairments associated with credit losses	$ 0	$ 0	$ 0
Interest earned on marketable securities	8,800,000	1,500,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest earned on marketable securities	8,800,000	$ 1,500,000
Cash and cash equivalents	$ 275,948,000			$ 189,052,000
Aggregate Fair Value \| Reverse repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents				$ 35,800,000

Fair Value Measurements - Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Less than one year, amortized cost	$ 787,710	$ 859,996
One to three years, amortized cost	716,571	734,338
Total amortized cost	1,504,281	1,594,334
Less than one year, aggregate fair value	788,246	861,181
One to three years, aggregate fair value	709,623	737,852
Total aggregate fair value	$ 1,497,869	$ 1,599,033

Fair Value Measurements - Convertible Senior Notes (Details) - Convertible senior notes, 0.25%, due 2023 - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	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	$ 768.2	$ 841.3

Property and Equipment - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property and Equipment
Total property and equipment	$ 243,827	$ 222,404
Less: accumulated depreciation and amortization	(92,883)	(81,148)
Total property and equipment, net	150,944	141,256
Capitalized internal-use software development costs
Property and Equipment
Total property and equipment	110,918	100,155
Data center equipment
Property and Equipment
Total property and equipment	22,018	22,009
Leasehold improvements
Property and Equipment
Total property and equipment	63,961	55,886
Office equipment
Property and Equipment
Total property and equipment	27,001	25,083
Furniture and fixtures
Property and Equipment
Total property and equipment	10,253	10,095
Software
Property and Equipment
Total property and equipment	$ 9,676	$ 9,176

Property and Equipment - Depreciation and Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 11.9	$ 7.6

Property and Equipment - Capitalized Software Development Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Capitalized internal use software development costs	$ 12,000	$ 7,000
Stock-based compensation capitalized in software development costs	3,418	1,623
Amortization of capitalized software development costs	$ 4,600	$ 3,800

Right-of-Use Asset and Lease Liabilities - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) property
Lessee, Lease, Description [Line Items]
Number of leased properties \| property	23
Renewal option	5 years
Operating lease, not yet commenced, liability	$ 43.5
Finance lease not yet commenced, liability	$ 0.7
Lease not yet commenced, term of contract	6 years 9 months 18 days
Maximum
Lessee, Lease, Description [Line Items]
Term of lease	9 years
Operating 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
	Mar. 31, 2020	Mar. 31, 2019
Leases [Abstract]
Operating lease cost	$ 10,424	$ 7,173
Finance lease cost:
Amortization of assets	1,904	1,163
Interest on lease liabilities	198	148
Short-term lease cost	1,412	1,435
Variable lease cost	1,296	487
Total net lease cost	$ 15,234	$ 10,406

Right-of-Use Asset and Lease Liabilities - Balance Sheet Classification of Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
ASSETS
Operating lease assets	$ 159,439	$ 156,741
Finance lease assets	12,866	14,770
Total leased assets	172,305	171,511
Current liabilities:
Operating	29,949	27,156
Finance	6,539	6,924
Noncurrent liabilities
Operating	140,120	139,200
Finance	7,250	8,746
Total lease liabilities	183,858	182,026
Operating lease accumulated amortization	31,200	23,200
Finance lease accumulated depreciation	$ 7,900	$ 6,000

Right-of-Use Asset and Lease Liabilities - Supplemental Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 9,953	$ 3,994
Operating cash flows from finance leases (interest)	198	148
Financing cash flows from finance leases	$ 1,881	$ 961
Weighted Average Remaining Lease Term [Abstract]
Operating leases	5 years 9 months 18 days	7 years 1 month 6 days
Finance leases	2 years 10 months 24 days	3 years 3 months 18 days
Weighted Average Discount Rate [Abstract]
Operating leases	5.70%	5.80%
Finance leases	5.30%	5.20%

Right-of-Use Asset and Lease Liabilities - Lease Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Maturity Of Operating Lease Liabilities
2020	$ 29,148
2021	38,190
2022	37,145
2023	29,378
2024	25,549
Thereafter	43,126
Total lease payments	202,536
Less: imputed interest	(32,467)
Total lease obligations	170,069
Less: current obligations	(29,949)	$ (27,156)
Long-term lease obligations	140,120	139,200
Maturity Of Finance Lease Liabilities
2020	5,507
2021	4,659
2022	2,333
2023	1,581
2024	315
Thereafter	581
Total lease payments	14,976
Less: imputed interest	(1,187)
Total lease obligations	13,789
Less: current obligations	(6,539)	(6,924)
Long-term lease obligations	$ 7,250	$ 8,746

Goodwill and Intangible Assets - Goodwill Rollforward (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Goodwill
Balance (beginning of period)	$ 2,296,784
Measurement period adjustments	(5,147)
Balance (end of period)	$ 2,291,637

Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortizable intangible assets:
Gross	$ 547,514	$ 543,442
Accumulated Amortization	(107,576)	(87,258)
Net	439,938	456,184
Intangible assets, gross	552,729	548,107
Total	445,153	460,849
Telecommunication licenses
Amortizable intangible assets:
Non-amortizable intangible assets:	4,920	4,370
Domain names
Amortizable intangible assets:
Non-amortizable intangible assets:	32	32
Trademarks and other
Amortizable intangible assets:
Non-amortizable intangible assets:	263	263
Developed technology
Amortizable intangible assets:
Gross	334,599	333,980
Accumulated Amortization	(67,259)	(55,390)
Net	267,340	278,590
Customer relationships
Amortizable intangible assets:
Gross	185,594	182,339
Accumulated Amortization	(33,296)	(26,347)
Net	152,298	155,992
Supplier relationships
Amortizable intangible assets:
Gross	4,356	4,356
Accumulated Amortization	(2,006)	(1,532)
Net	2,350	2,824
Trade names
Amortizable intangible assets:
Gross	20,060	20,060
Accumulated Amortization	(4,727)	(3,727)
Net	15,333	16,333
Patent
Amortizable intangible assets:
Gross	2,905	2,707
Accumulated Amortization	(288)	(262)
Net	$ 2,617	$ 2,445

Goodwill and Intangible Assets - Amortization Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 20.3	$ 13.6

Goodwill and Intangible Assets - Total Estimated Future Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Intangible Assets
2020	$ 60,796
2021	80,480
2022	77,865
2023	74,583
2024	69,304
Thereafter	76,910
Net	$ 439,938	$ 456,184

Accrued Expenses and Other Liabilities - Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued Liabilities and Other Liabilities [Abstract]
Accrued payroll and related	$ 30,198	$ 20,462
Accrued bonus and commission	11,052	12,898
Accrued cost of revenue	71,479	47,563
Sales and other taxes payable	29,758	28,592
ESPP contributions	11,521	4,023
VAT and other taxes	4,152	4,838
Acquisition holdback	4,520	6,520
Accrued other expense	32,713	22,785
Total accrued expenses and other current liabilities	$ 195,393	$ 147,681

Accrued Expenses and Other Liabilities - Long-term Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued Liabilities and Other Liabilities [Abstract]
Deferred tax liability	$ 8,362	$ 7,535
Acquisition holdback	3,750	3,750
Accrued other expenses	8,854	6,462
Total other long-term liabilities	$ 20,966	$ 17,747

Notes Payable - Issuance (Details) - USD ($)	1 Months Ended
Notes Payable - Issuance (Details) - USD ($)	May 31, 2018	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Convertible senior notes, 0.25%, due 2023
Debt Instrument [Line Items]
Aggregate principal amount		$ 549,998,000	$ 549,999,000	$ 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	3 Months Ended
	May 31, 2018 USD ($) $ / shares	Mar. 31, 2020 USD ($) D $ / shares	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) \| $ / shares		$ 0.001	$ 0.001
Effective percentage		5.70%
Common Class A
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) \| $ / shares	$ 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 \| $			$ 119,434	$ 119,435
Debt issuance costs \| $	$ 10,200	$ 6,678	$ 7,162
Convertible senior notes, 0.25%, due 2023 \| Common Class A
Debt Instrument [Line Items]
Conversion ratio	14.104
Capped calls
Debt Instrument [Line Items]
Initial strike price (in dollars per share) \| $ / shares	$ 70.90

Notes Payable - Net Carrying Amount (Details) - Convertible senior notes, 0.25%, due 2023 - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	May 31, 2018
Net carrying amount of the liability component of the Notes
Aggregate principal amount	$ 549,998,000		$ 549,999,000	$ 550,000,000.0
Unamortized discount	(78,953,000)		(84,647,000)
Unamortized issuance costs	(6,678,000)		(7,162,000)		$ (10,200,000)
Net carrying amount	464,367,000		458,190,000
Net carrying amount of the equity component of the Notes
Proceeds allocated to the conversion options (debt discount)			119,434,000	$ 119,435,000
Issuance costs	(2,819,000)	$ (2,819,000)
Net carrying amount	$ 116,615,000		$ 116,616,000

Notes Payable - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Interest expense recognized related to the Notes
Contractual interest expense	$ 344	$ 344
Amortization of debt issuance costs	484	458
Amortization of debt discount	5,694	5,383
Total interest expense related to the Notes	$ 6,522	$ 6,185

Notes Payable - Capped Calls (Details) - Capped calls $ / shares in Units, $ in Millions	1 Months Ended
	May 31, 2018 USD ($) $ / shares shares
Capped calls
Initial strike price (in dollars per share)	$ 70.90
Initial cap price (in dollars per share)	$ 105.04
Number of shares covered \| shares	7,757,158
Net cost to purchase the transactions \| $	$ 58.5

Supplemental Balance Sheet Information - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Allowance for doubtful accounts
Balance, beginning of period	$ 6,287	$ 4,945
Additions	4,261	(245)
Write-offs	(1,463)	(419)
Balance, end of period	$ 9,085	$ 4,281
Reserve for allowance for doubtful account	2.00%	2.00%

Supplemental Balance Sheet Information - Sales Credit Reserve (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Sales credit reserve
Balance, beginning of period	$ 6,784	$ 3,015
Additions	8,174	2,681
Deductions against reserve	(5,271)	(2,865)
Balance, end of period	$ 9,687	$ 2,831
Sales credit reserve, percent of revenue	3.00%	1.00%

Revenue by Geographic Area - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Abstract]
Revenue	$ 364,868	$ 233,139
United States
Disaggregation of Revenue [Abstract]
Revenue	261,813	166,553
International
Disaggregation of Revenue [Abstract]
Revenue	$ 103,055	$ 66,586

Revenue by Geographic Area - Percentage of Revenue by Geographic Area (Details) - Revenue from Contract with Customer Benchmark - Geographic Concentration Risk	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
United States
Risks and Uncertainties [Abstract]
Percentage of revenue (as a percent)	72.00%	71.00%
International
Risks and Uncertainties [Abstract]
Percentage of revenue (as a percent)	28.00%	29.00%

Commitments and Contingencies - Other Commitments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Long-term Purchase Commitment [Line Items]
Unrecorded unconditional purchase obligation	$ 16.8
Maximum
Long-term Purchase Commitment [Line Items]
Term of lease	9 years
Term of non-cancellable agreement	2 years

Commitments and Contingencies - Indemnification Agreements (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Indemnification Agreements
Loss Contingencies [Line Items]
Amount accrued	$ 0	$ 0

Commitments and Contingencies - Other taxes (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Liability for uncertain tax positions	$ 27.5	$ 27.0

Stockholders' Equity - Preferred Stock (Details) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
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) - $ / shares	Mar. 31, 2020	Dec. 31, 2019	May 31, 2018
Common Stock
Common stock, par value (in dollars per share)	$ 0.001	$ 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)			$ 0.001
Common stock, issued (in shares)	128,606,443	126,882,172
Common stock, outstanding (in shares)	128,606,443	126,882,172
Common Class B
Common Stock
Common stock, authorized (in shares)	100,000,000	100,000,000
Common stock, issued (in shares)	11,356,940	11,530,627
Common stock, outstanding (in shares)	11,356,940	11,530,627

Stockholders' Equity - Common Stock Shares Reserved (Details) - shares	Mar. 31, 2020	Dec. 31, 2019
Stockholders' Equity
Total (in shares)	53,009,614	46,270,890
2016 Stock Option and Incentive Plan
Stockholders' Equity
Stock-based awards available for grant under 2016 Plan (in shares)	20,998,004	14,957,734
Common Class A
Stockholders' Equity
Class A common stock reserved for Twilio.org (in shares)	773,571	795,673
Class A common stock reserved for the convertible senior notes (in shares)	10,472,165	10,472,165
Stock options issued and outstanding
Stockholders' Equity
Stock options issued and outstanding (in shares)	7,492,970	7,705,848
Nonvested restricted stock units issued and outstanding
Stockholders' Equity
Nonvested restricted stock units issued and outstanding (in shares)	8,039,823	8,490,517
Class A common stock committed under 2016 ESPP
Stockholders' Equity
Stock-based awards available for grant under 2016 Plan (in shares)	5,233,081	3,848,953

Stock-Based Compensation - 2008 Stock Option Plan (Details)	Mar. 31, 2020 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			3 Months Ended
	Jan. 01, 2020	Jan. 01, 2019	Mar. 31, 2020	Jun. 21, 2016
Stock Based Compensation
Increase in shares available for grant (in shares)	1,384,128	1,000,802
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)	6,920,640	5,004,011
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
	Jan. 01, 2020	Jan. 01, 2019	Mar. 31, 2020	Jun. 21, 2016
Stock Based Compensation
Increase in shares available for grant (in shares)	1,384,128	1,000,802
Unrecognized compensation cost, other than options			$ 1.3
Weighted-average period (in years)			1 month 6 days
Class A common stock committed under 2016 ESPP
Stock Based Compensation
Maximum automatic annual increase (in shares)			1,800,000
Maximum automatic annual increase as a percentage of outstanding common shares			1.00%
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%

Stock-Based Compensation - Stock Option Activity (Details) - Employee and nonemployee stock options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Number of options outstanding
Outstanding options as of the beginning of the period (in shares)	7,150,848
Granted (in shares)	534,412
Exercised (in shares)	(669,030)
Forfeited and cancelled (in shares)	(78,260)
Outstanding options as of the end of the period (in shares)	6,937,970
Weighted- average exercise price (Per share)
Outstanding options as of the beginning of the period (in dollars per share)	$ 28.79
Granted (in dollars per share)	121.20
Exercised (in dollars per share)	12.30
Forfeited and cancelled (in dollars per share)	52.44
Outstanding options as of the end of the period (in dollars per share)	$ 37.23
Weighted- average remaining contractual term (In years)
Weighted-average remaining contractual term (in years)	7 years 1 month 28 days	6 years 5 months 19 days
Aggregate intrinsic value	$ 400,612		$ 511,971
Options vested and exercisable and options vested and expected to vest
Options vested and exercisable - number of options outstanding (in shares)	4,545,317
Options vested and exercisable - weighted-average exercise price (in dollars per share)	$ 18.07
Options vested and exercisable - weighted-average remaining contractual term	6 years 4 months 20 days
Options vested and exercisable - aggregate intrinsic value	$ 329,352

Stock-Based Compensation - Stock Options - Additional Information (Details) - Employee and nonemployee stock options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock Based Compensation
Aggregate intrinsic value of stock options exercised	$ 68,359	$ 187,016
Total estimated grant date fair value of options vested	$ 23,335	$ 55,310
Weighted-average grant date fair value per share of options granted (in dollars per share)	$ 60.47	$ 58.00

Stock-Based Compensation - Performance-Based Stock Options (Details) $ / shares in Units, $ in Thousands		3 Months Ended
	Feb. 28, 2017 USD ($) award $ / shares shares	Mar. 31, 2020 USD ($) $ / shares shares	Mar. 31, 2019	Dec. 31, 2019 USD ($)
Performance-based stock options
Stock-Based Compensation
Number of distinct awards \| award	3
Total grant value \| $	$ 5,900
Vesting period upon satisfaction of performance condition	2 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
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
Weighted-average remaining contractual term
Weighted-average remaining contractual term (in years)		3 years 10 months 28 days	4 years 1 month 28 days
Aggregate intrinsic value \| $		$ 32,062		$ 36,941
Options vested and exercisable
Options vested and exercisable - number of options outstanding (in shares) \| shares		462,499
Options vested and exercisable - weighted-average exercise price (in dollars per share)		$ 31.72
Options vested and exercisable - weighted-average remaining contractual term		3 years 10 months 28 days
Options vested and exercisable - aggregate intrinsic value \| $		$ 26,719
$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 4 months 24 days

Stock-Based Compensation - Stock Options - Unrecognized Compensation Cost (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Stock Based Compensation
Weighted-average period (in years)	1 month 6 days
Stock options issued and outstanding
Stock Based Compensation
Unrecognized compensation cost, options	$ 109.1
Weighted-average period (in years)	2 years 1 month 6 days

Stock-Based Compensation - Restricted Stock Units Activity (Details) - Nonvested restricted stock units issued and outstanding - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Number of awards outstanding
Nonvested RSUs at the beginning of the period (in shares)	8,490,517
Granted (in shares)	728,343
Vested (in shares)	(872,870)
Forfeited and canceled (in shares)	(306,167)
Nonvested RSUs at the end of the period (in shares)	8,039,823
Weighted- average grant date fair value (Per share)
Nonvested RSUs at the beginning of the period (in dollars per share)	$ 74.21
Granted (in dollars per share)	117.09
Vested (in dollars per share)	62.65
Forfeited and canceled (in dollars per share)	75.56
Nonvested RSUs at the end of the period (in dollars per share)	$ 80.61
Aggregate intrinsic value (In thousands)
Aggregate intrinsic value	$ 713,474	$ 830,167

Stock-Based Compensation - Restricted Stock Units - Unrecognized Compensation Cost (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Stock Based Compensation
Unrecognized compensation cost, other than options	$ 1.3
Weighted-average period (in years)	1 month 6 days
Nonvested restricted stock units issued and outstanding
Stock Based Compensation
Unrecognized compensation cost, other than options	$ 579.9
Weighted-average period (in years)	2 years 7 months 6 days

Stock-Based Compensation - Valuation Assumptions (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee stock options
Valuation Assumptions
Expected term (in years)	6 years 29 days
Expected volatility, low end of range (as a percent)	51.90%	48.30%
Expected volatility, high end of range (as a percent)	51.90%	66.50%
Risk-free interest rate, low end of range (as a percent)	1.30%	2.40%
Risk-free interest rate, high end of range (as a percent)	1.40%	2.50%
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)	$ 31.7
Minimum \| Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)	117.9	$ 111.3
Expected term (in years)		3 months 29 days
Maximum \| Employee stock options
Valuation Assumptions
Fair value of common stock (in dollars per share)	$ 126.7	$ 130.7
Expected term (in years)		6 years 29 days

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock-Based Compensation Expense
Stock-based compensation expense	$ 69,025	$ 58,324
Cost of revenue
Stock-Based Compensation Expense
Stock-based compensation expense	1,837	1,809
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense	33,209	25,339
Sales and marketing
Stock-Based Compensation Expense
Stock-based compensation expense	19,943	11,749
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense	$ 14,036	$ 19,427

Net Loss per Share Attributable to Common Stockholders - General Information (Details) - Vote	Mar. 31, 2020	Dec. 31, 2019
Common Class A
Net Loss Per Share Attributable to Common Stockholders
Votes per share	1	1
Common Class B
Net Loss Per Share Attributable to Common Stockholders
Votes per share	10	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
	Mar. 31, 2020	Mar. 31, 2019
Net Loss Per Share Attributable to Common Stockholders
Net loss attributable to common stockholders (in thousands)	$ (94,791)	$ (36,503)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)	139,231,594	116,590,513
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.68)	$ (0.31)

Net Loss Per Share Attributable to Common Stockholders - Anti-Dilutive Securities (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Anti-dilutive securities
Antidilutive securities (in shares)	19,266,388	22,624,271
Conversion price (in dollars per share)	$ 70.90
Stock options issued and outstanding
Anti-dilutive securities
Antidilutive securities (in shares)	7,492,970	10,045,155
Nonvested restricted stock units issued and outstanding
Anti-dilutive securities
Antidilutive securities (in shares)	8,039,823	8,813,737
Class A common stock reserved for Twilio.org
Anti-dilutive securities
Antidilutive securities (in shares)	773,571	776,334
Class A common stock committed under 2016 ESPP
Anti-dilutive securities
Antidilutive securities (in shares)	212,028	113,959
Conversion spread
Anti-dilutive securities
Antidilutive securities (in shares)	2,747,996	2,873,836
Unvested shares subject to repurchase
Anti-dilutive securities
Antidilutive securities (in shares)	0	1,250

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 977	$ (51,721)
Business Acquisition [Line Items]
Release of valuation allowance on deferred tax assets		51,600
SendGrid
Business Acquisition [Line Items]
Release of valuation allowance on deferred tax assets		$ 49,200