Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2019	Nov. 01, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-36180
Entity Registrant Name	CHEGG, INC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-3237489
Entity Address, Address Line One	3990 Freedom Circle
Entity Address, City or Town	Santa Clara
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95054
City Area Code	408
Local Phone Number	855-5700
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	CHGG
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		120,981,819
Entity Central Index Key	0001364954
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 450,457	$ 374,664
Short-term investments	345,392	93,345
Accounts receivable, net of allowance for doubtful accounts of $31 and $229 at September 30, 2019 and December 31, 2018, respectively	13,678	12,733
Prepaid expenses	9,654	4,673
Other current assets	24,888	9,510
Total current assets	844,069	494,925
Long-term investments	340,118	16,052
Property and equipment, net	77,667	59,904
Goodwill	149,068	149,524
Intangible assets, net	20,622	25,915
Right of use assets	16,312	0
Other assets	15,836	14,618
Total assets	1,463,692	760,938
Current liabilities
Accounts payable	4,197	8,177
Deferred revenue	27,457	17,418
Current operating lease liabilities	4,982	0
Accrued liabilities	52,199	34,077
Total current liabilities	88,835	59,672
Long-term liabilities
Convertible senior notes, net	887,215	283,668
Long-term operating lease liabilities	15,315	0
Other long-term liabilities	3,815	6,964
Total long-term liabilities	906,345	290,632
Total liabilities	995,180	350,304
Commitments and contingencies (Note 9)
Stockholders' equity:
Preferred stock, $0.001 par value – 10,000,000 shares authorized, no shares issued and outstanding	0	0
Common stock, $0.001 par value 400,000,000 shares authorized; 120,668,843 and 115,500,418 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	121	116
Additional paid-in capital	894,660	818,113
Accumulated other comprehensive loss	(1,758)	(1,019)
Accumulated deficit	(424,511)	(406,576)
Total stockholders' equity	468,512	410,634
Total liabilities and stockholders' equity	$ 1,463,692	$ 760,938

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable, current	$ 31	$ 229
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	120,668,843	115,500,418
Common stock, shares outstanding	120,668,843	115,500,418

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net revenues	$ 94,151	$ 74,237	$ 285,422	$ 225,408
Cost of revenues	22,164	19,918	66,017	57,926
Gross profit	71,987	54,319	219,405	167,482
Operating expenses:
Research and development	36,442	29,045	101,199	80,796
Sales and marketing	16,822	15,690	47,334	42,463
General and administrative	23,752	20,000	70,044	57,735
Restructuring charges	28	17	97	252
Total operating expenses	77,044	64,752	218,674	181,246
(Loss) income from operations	(5,057)	(10,433)	731	(13,764)
Interest expense, net and other income, net:
Interest expense, net	(13,548)	(3,772)	(31,294)	(7,456)
Other income, net	7,751	1,209	14,571	2,667
Total interest expense, net and other income, net	(5,797)	(2,563)	(16,723)	(4,789)
Loss before provision for income taxes	(10,854)	(12,996)	(15,992)	(18,553)
Provision for income taxes	623	713	1,832	1,682
Net loss	$ (11,477)	$ (13,709)	$ (17,824)	$ (20,235)
Net loss per share, basic and diluted (in dollars per share)	$ (0.10)	$ (0.12)	$ (0.15)	$ (0.18)
Weighted average shares used to compute net loss per share, basic and diluted (in shares)	120,085	114,184	118,547	112,621

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (11,477)	$ (13,709)	$ (17,824)	$ (20,235)
Other comprehensive loss:
Change in net unrealized loss on available for sale investments, net of tax	(73)	43	379	66
Change in foreign currency translation adjustments, net of tax	(1,067)	(347)	(1,118)	(749)
Other comprehensive loss	(1,140)	(304)	(739)	(683)
Total comprehensive loss	$ (12,617)	$ (14,013)	$ (18,563)	$ (20,918)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Common stock, beginning balance (in shares) at Dec. 31, 2017		109,668,000
Beginning balance at Dec. 31, 2017	$ 391,062	$ 110	$ 782,845	$ (282)	$ (391,611)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity component of convertible senior notes, net of issuance costs	62,444		62,444
Purchase of convertible senior notes capped call	(39,227)		(39,227)
Repurchase of common stock (in shares)		(983,000)
Repurchase of common stock	(20,000)	$ (1)	(19,999)
Issuance of common stock upon exercise of stock options and ESPP (in shares)		2,799,000
Issuance of common stock upon exercise of stock options and ESPP	23,461	$ 3	23,458
Net issuance of common stock for settlement of RSUs (in shares)		3,080,000
Net issuance of common stock for settlement of RSUs	(45,666)	$ 3	(45,669)
Warrant exercises (in shares)		34,000
Warrant exercises	0		0
Share-based compensation expense	37,503		37,503
Other comprehensive income (loss)	(683)			(683)
Net loss	(20,235)				(20,235)
Common stock, ending balance (in shares) at Sep. 30, 2018		114,598,000
Beginning balance at Sep. 30, 2018	388,582	$ 115	801,355	(965)	(411,923)
Common stock, beginning balance (in shares) at Jun. 30, 2018		113,551,000
Beginning balance at Jun. 30, 2018	388,719	$ 114	787,480	(661)	(398,214)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and ESPP (in shares)		765,000
Issuance of common stock upon exercise of stock options and ESPP	5,413	$ 1	5,412
Net issuance of common stock for settlement of RSUs (in shares)		282,000
Net issuance of common stock for settlement of RSUs	(5,355)	$ 0	(5,355)
Share-based compensation expense	13,818		13,818
Other comprehensive income (loss)	(304)			(304)
Net loss	(13,709)				(13,709)
Common stock, ending balance (in shares) at Sep. 30, 2018		114,598,000
Beginning balance at Sep. 30, 2018	$ 388,582	$ 115	801,355	(965)	(411,923)
Common stock, beginning balance (in shares) at Dec. 31, 2018	115,500,418	115,500,000
Beginning balance at Dec. 31, 2018	$ 410,634	$ 116	818,113	(1,019)	(406,576)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity component of convertible senior notes, net of issuance costs	206,747		206,747
Purchase of convertible senior notes capped call	(97,200)		(97,200)
Repurchase of common stock (in shares)		(504,000)
Repurchase of common stock	(20,000)	$ (1)	(19,999)
Issuance of common stock upon exercise of stock options and ESPP (in shares)		2,545,000
Issuance of common stock upon exercise of stock options and ESPP	27,720	$ 3	27,717
Net issuance of common stock for settlement of RSUs (in shares)		3,064,000
Net issuance of common stock for settlement of RSUs	(91,073)	$ 3	(91,076)
Issuance of common stock in connection with acquisition (in shares)		64,000
Issuance of common stock in connection with prior acquisition	3,003		3,003
Share-based compensation expense	47,355		47,355
Other comprehensive income (loss)	(739)			(739)
Net loss	$ (17,824)				(17,824)
Common stock, ending balance (in shares) at Sep. 30, 2019	120,668,843	120,669,000
Beginning balance at Sep. 30, 2019	$ 468,512	$ 121	894,660	(1,758)	(424,511)
Common stock, beginning balance (in shares) at Jun. 30, 2019		119,336,000
Beginning balance at Jun. 30, 2019	459,571	$ 119	873,104	(618)	(413,034)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and ESPP (in shares)		991,000
Issuance of common stock upon exercise of stock options and ESPP	11,674	$ 1	11,673
Net issuance of common stock for settlement of RSUs (in shares)		319,000
Net issuance of common stock for settlement of RSUs	(8,824)	$ 1	(8,825)
Issuance of common stock in connection with acquisition (in shares)		23,000
Issuance of common stock in connection with prior acquisition	1,843		1,843
Share-based compensation expense	16,865		16,865
Other comprehensive income (loss)	(1,140)			(1,140)
Net loss	$ (11,477)				(11,477)
Common stock, ending balance (in shares) at Sep. 30, 2019	120,668,843	120,669,000
Beginning balance at Sep. 30, 2019	$ 468,512	$ 121	$ 894,660	$ (1,758)	$ (424,511)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (17,824)	$ (20,235)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization expense	21,369	16,631
Share-based compensation expense	47,355	37,503
Loss from write-off of property and equipment	832	29
Amortization of debt discount and issuance costs	30,114	6,958
Deferred income taxes	59	(315)
Operating lease expense, net of accretion	3,284	0
Other non-cash items	(370)	51
Change in assets and liabilities:
Accounts receivable	(850)	2,409
Prepaid expenses and other current assets	(20,741)	(24,250)
Other assets	1,989	(587)
Accounts payable	(3,983)	(3,001)
Deferred revenue	10,039	11,841
Accrued liabilities	18,095	16,044
Other liabilities	(2,793)	1,589
Net cash provided by operating activities	86,575	44,667
Cash flows from investing activities
Purchases of investments	(822,869)	(113,276)
Proceeds from sale of investments	53,261	1,800
Maturities of investments	190,744	118,080
Purchases of property and equipment	(31,520)	(18,048)
Acquisition of businesses, net of cash acquired	0	(34,650)
Net cash used in investing activities	(610,384)	(46,094)
Cash flows from financing activities
Common stock issued under stock plans, net	27,723	23,463
Payment of taxes related to the net share settlement of equity awards	(91,076)	(45,669)
Proceeds from issuance of convertible senior notes, net of issuance costs	780,180	335,618
Purchase of convertible senior notes capped call	(97,200)	(39,227)
Repurchase of common stock	(20,000)	(20,000)
Net cash provided by financing activities	599,627	254,185
Net increase in cash, cash equivalents and restricted cash	75,818	252,758
Cash, cash equivalents and restricted cash, beginning of period	375,945	126,963
Cash, cash equivalents and restricted cash, end of period	451,763	379,721
Supplemental cash flow data:
Interest	901	55
Income taxes	1,492	1,560
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	3,847	0
Right of use assets obtained in exchange for lease obligations, operating leases	2,638	0
Non-cash investing and financing activities:
Accrued purchases of long-lived assets	4,452	2,993
Issuance of common stock related to prior acquisition	$ 3,003	$ 0

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - Reconciliation of cash, cash equivalents and restricted cash - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Statement of Cash Flows [Abstract]
Cash and cash equivalents	$ 450,457	$ 379,020
Restricted cash included in other current assets	125	0
Restricted cash included in other assets	1,181	701
Total cash, cash equivalents and restricted cash	$ 451,763	$ 379,721

Background and Basis of Presentation	9 Months Ended
Background and Basis of Presentation	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background and Basis of Presentation	Background and Basis of Presentation Company and Background Chegg, Inc. (Chegg, the Company, we, us, or our), headquartered in Santa Clara, California, was incorporated as a Delaware corporation in July 2005. Chegg is a smarter way to student. As the leading direct-to-student learning platform, we strive to improve educational outcomes by putting the student first in all our decisions. We support students on their journey from high school to college and into their career with tools designed to help them pass their test, pass their class, and save money on required materials. Our services are available online, anytime and anywhere, so we can reach students when they need us most. Basis of Presentation The accompanying condensed consolidated balance sheet as of September 30, 2019, the condensed consolidated statements of operations, the condensed consolidated statements of comprehensive loss, and the condensed consolidated statements of stockholder's equity for the three and nine months ended September 30, 2019 and 2018, the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018 and the related footnote disclosures are unaudited. In the opinion of management, the accompanying unaudited condensed consolidated financial statements contain all adjustments, including normal recurring adjustments, necessary to present fairly our financial position as of September 30, 2019, our results of operations, results of comprehensive loss, and stockholder's equity for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018. Our results of operations, stockholder's equity, and cash flows for the nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the full year. We operate in a single segment. Our fiscal year ends on December 31 and in this report we refer to the year ended December 31, 2018 as 2018. The condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto that are included in our Annual Report on Form 10-K for the year ended December 31, 2018 (the Annual Report on Form 10-K) filed with the U.S. Securities and Exchange Commission (SEC). We have changed the captions on our condensed consolidated statements of cash flows from “purchases of marketable securities” to “purchases of investments” and from “maturities of marketable securities” to “maturities of investments.” This change does not impact any current or previously reported results. Except for our policies on leases and convertible senior notes, there have been no material changes to our significant accounting policies as compared to the significant accounting policies described in our Annual Report on Form 10-K. Leases We determine if an arrangement is a lease at inception. Operating leases are included in operating lease right of use (ROU) assets, operating lease liabilities within current liabilities, and operating lease liabilities within long-term liabilities on our condensed consolidated balance sheet. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. Our leases do not provide an implicit rate and therefore we use our incremental borrowing rate based on the information available at commencement date in determining the present value of future minimum lease payments. Our incremental borrowing rate is estimated based on the estimated rate incurred to borrow, on a collateralized basis over a similar term as our leases, an amount equal to the lease payments in a similar economic environment. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise such options. We do not record leases on our condensed consolidated balance sheet with a term of one year or less. We do not separate lease and non-lease components but rather account for each separate component as a single lease component for all underlying classes of assets. Some of our leases include payments that are dependent on an index, such as the Consumer Price Index (CPI), and our minimum lease payments include payments based on the index at inception with any future changes in such indices recognized as an expense in the period of change. Where leases contain escalation clauses, rent abatements, or concessions, such as rent holidays and landlord or tenant incentives or allowances, we apply them in the determination of straight-line operating lease cost over the lease term. Convertible Senior Notes, net In March 2019, we issued $700 million in aggregate principal amount of 0.125% convertible senior notes due in 2025 (2025 notes) and in April 2019, the initial purchasers fully exercised their option to purchase $100 million of additional 2025 notes for aggregate total gross proceeds of $800 million. In April 2018, we issued $345 million in aggregate principal amount of 0.25% convertible senior notes due in 2023 (2023 notes). Collectively, the 2025 notes and the 2023 notes are referred to as the “notes.” In accounting for their issuance, we separated the notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of similar liabilities that do not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was determined by deducting the carrying amount of the liability component from the par value of the notes. The difference represents the debt discount, recorded as a reduction of the convertible senior notes on our condensed consolidated balance sheets, and is amortized to interest expense over the term of the notes using the effective interest rate method. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. In accounting for the issuance costs related to the notes, we allocated the total amount of issuance costs incurred to liability and equity components based on their relative values. Issuance costs attributable to the liability component are being amortized on a straight-line basis, which approximates the effective interest rate method, to interest expense over the term of the notes. The issuance costs attributable to the equity component are recorded as a reduction of the equity component within additional paid-in capital. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States (U.S. GAAP) requires management to make estimates, judgments, and assumptions that affect the reported amounts of assets and liabilities; the disclosure of contingent liabilities at the date of the financial statements; and the reported amounts of revenues and expenses during the reporting periods. Significant estimates, assumptions, and judgments are used for, but not limited to: revenue recognition, recoverability of accounts receivable, restructuring charges, share-based compensation expense including estimated forfeitures, accounting for income taxes, useful lives assigned to long-lived assets for depreciation and amortization, impairment of goodwill and long-lived assets, the valuation of acquired intangible assets, the valuation of our convertible senior notes, and operating lease ROU assets and operating lease liabilities. We base our estimates on historical experience, knowledge of current business conditions, and various other factors we believe to be reasonable under the circumstances. These estimates are based on management’s knowledge about current events and expectations about actions we may undertake in the future. Actual results could differ from these estimates, and such differences could be material to our financial position and results of operations. Recent Accounting Pronouncements Recently Issued Accounting Pronouncements Not Yet Adopted In May 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief. ASU 2019-05 provides entities with an option to irrevocably elect the fair value option for eligible instruments. 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. ASU 2019-04 provides codification updates to ASU 2016-01 and ASU 2016-13. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. ASU 2016-13 replaces the existing incurred loss impairment model for trade receivables with an expected loss model which requires the use of forward-looking information to calculate expected credit loss estimates. Additionally, the concept of other-than-temporary impairment for available-for-sale investments is eliminated and instead ASU 2016-13 requires an entity to focus on determining whether any impairment is a result of a credit loss or other factors. It also requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction to the amortized cost basis. These changes may result in earlier recognition of credit losses. Early adoption is permitted and these guidance updates require a modified retrospective method of adoption, though a prospective method of adoption is required for available-for-sale debt securities for which an other-than-temporary impairment had been recognized before the effective date. These guidance updates are effective for annual periods beginning after December 15, 2019. We plan to adopt this guidance on January 1, 2020 and we are currently in the process of evaluating the impact of these guidance updates. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with existing guidance contained within subtopic 350-40 to develop or obtain internal-use software. Early adoption is permitted and the guidance allows for a retrospective or prospective application. The guidance is effective for annual periods beginning after December 15, 2019. We plan to adopt this guidance on January 1, 2020 under the prospective application and we are currently in the process of evaluating the impact of this guidance. In July 2018, the FASB issued ASU 2018-09, Codification Improvements. ASU 2018-09 provides updates for technical corrections, clarifications, and other minor improvements to a wide variety of topics in the ASC. The transition method of adoption is dependent on the ASC topic impacted by this guidance. Additionally, some of the ASC topic updates are effective upon issuance of ASU 2018-09 and some of the ASC topic updates are effective at a future date. The ASC topic updates effective upon issuance of ASU 2018-09 do not impact our accounting for the respective ASC topics. For those ASC topic updates effective at a future date, we are currently in the process of evaluating the impact of this guidance update. Recently Adopted Accounting Pronouncements The FASB has issued four ASUs related to Accounting Standards Codification (ASC) 842. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements and ASU 2018-10, Codification Improvements to Topic 842, Leases. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASC 842 requires an entity to recognize a ROU asset and lease liability for all leases with terms of more than 12 months. Recognition, measurement, and presentation of expenses will depend on classification as a finance or operating lease. The amendments in this update also require certain quantitative and qualitative disclosures about leasing arrangements. We have adopted ASC 842 on January 1, 2019 and have elected the transition method of adoption that allows for a modified retrospective adoption with a cumulative-effect adjustment to the opening balance of accumulated deficit and recorded an immaterial decrease to our opening balance of accumulated deficit. As a result, we have not changed previously disclosed amounts or provided additional disclosures for comparative periods. We initially recorded ROU assets of $17.2 million and lease liabilities of $21.1 million on our condensed consolidated balance sheet. ASC 842 does not have a material impact to our condensed consolidated statements of operations. We have elected a package of transition practical expedients which include not reassessing whether any expired or existing contracts are or contain leases, not reassessing the lease classification of expired or existing leases, and not reassessing initial direct costs for existing leases. We have also elected a practical expedient to not separate lease and non-lease components. We did not elect the practical expedient to use hindsight in determining our lease terms or assessing impairment of our ROU assets. See Note 8. Leases for more information.

Revenues

9 Months Ended

Sep. 30, 2019

Revenue from Contract with Customer [Abstract]

Revenues

Revenue Recognition

Revenues are recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. The majority of our revenues are recognized over time as services are performed, with certain revenues, most significantly the revenue share we earn from our print textbook partners, being recognized at the point in time when print textbooks are shipped to students.

The following tables set forth our total net revenues for the periods shown disaggregated for our Chegg Services and Required Materials product lines (in thousands, except percentages):



	Three Months Ended September 30,				Change
	2019		2018		$		%
Chegg Services	$	69,304	$	54,201	$	15,103	28	%
Required Materials	24,847		20,036		4,811		24
Total net revenues	$	94,151	$	74,237	$	19,914	27



	Nine Months Ended September 30,				Change
	2019		2018		$		%
Chegg Services	$	224,903	$	172,327	$	52,576	31	%
Required Materials	60,519		53,081		7,438		14
Total net revenues	$	285,422	$	225,408	$	60,014	27

During the three months ended September 30, 2019, we recognized $15.7 million of revenues that were included in our deferred revenue balance as of June 30, 2019. During the nine months ended September 30, 2019, we recognized $16.0 million of revenues that were included in our deferred revenue balance as of December 31, 2018. During the three and nine months ended September 30, 2019, we recognized $2.2 million and $2.7 million, respectively, of previously deferred revenues recognized from performance obligations satisfied in previous periods related to variable consideration recognized from our agreement with our Required Materials print textbook partner. The aggregate amount of unsatisfied performance obligations is approximately $29.0 million as of September 30, 2019, of which substantially all is expected to be recognized into revenues over the next year and the remainder within two years.

Contract Balances

The following table presents our accounts receivable, net and deferred revenue balances (in thousands, except percentages):



					Change
	September 30, 2019		December 31, 2018		$		%
Accounts receivable, net	$	13,678	$	12,733	$	945	7	%
Deferred revenue	$	27,457	$	17,418	$	10,039	58	%

During the nine months ended September 30, 2019, our accounts receivable, net balance increased by $0.9 million, or 7%, primarily due to timing of billings partially offset by an improvement in cash collections. During the nine months ended September 30, 2019, our deferred revenue balance increased by $10.0 million, or 58%, primarily due to increased bookings for our Chegg Study service and eTextbook rentals driven by the seasonality of our business. We had no contract assets as of September 30, 2019 and an immaterial amount as of December 31, 2018.

Net Loss Per Share

9 Months Ended

Sep. 30, 2019

Earnings Per Share [Abstract]

Net Loss Per Share

Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential shares of common stock, including stock options, restricted stock units (RSUs), performance-based restricted stock units (PSUs), and shares related to convertible senior notes, to the extent dilutive. Basic and diluted net loss per share was the same for each period presented as the inclusion of all potential common shares outstanding would have been anti-dilutive.

The following table sets forth the computation of basic and diluted net loss per share (in thousands, except per share amounts):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2019			2018			2019			2018
Numerator:
Net loss	$	(11,477	)	$	(13,709	)	$	(17,824	)	$	(20,235	)
Denominator:
Weighted average shares used to compute net loss per share, basic and diluted	120,085			114,184			118,547			112,621

Net loss per share, basic and diluted	$	(0.10	)	$	(0.12	)	$	(0.15	)	$	(0.18	)

The following potential weighted-average shares of common stock outstanding were excluded from the computation of diluted net loss per share because including them would have been anti-dilutive (in thousands):



	Three Months Ended September 30,		Nine Months Ended September 30,
	2019	2018	2019	2018
Options to purchase common stock	2,122	3,961	2,715	4,282
RSUs and PSUs	3,831	7,479	4,952	8,075
Shares related to convertible senior notes	4,098	1,221	3,709	—
Employee stock purchase plan	7	17	3	12
Total common stock equivalents	10,058	12,678	11,379	12,369

Shares related to convertible senior notes represents the anti-dilutive impact of our issuance of $345 million in aggregate principal amount of our 2023 notes as the average price of our common stock during the three and nine months ended September 30, 2019 was higher than the conversion price of $26.95. While these shares are anti-dilutive during the three and nine months ended September 30, 2019, they may be dilutive in periods we report net income. However, as a result of the capped call transactions, there will be no economic dilution from the 2023 notes up to $40.68, as exercise of the capped call instruments will reduce dilution from the 2023 notes that would have otherwise occurred when the average price of our common stock exceeds the conversion price. None of the shares related to our issuance of $800 million in aggregate principal amount of our 2025 notes were anti-dilutive during the three and nine months ended September 30, 2019. The average price of our common stock during the three and nine months ended September 30, 2019 was lower than the conversion price of our 2025 notes of $51.56. See Note 7, Convertible Senior Notes, for more information about our convertible senior notes.

Cash and Cash Equivalents, and Investment

9 Months Ended

Sep. 30, 2019

Cash and Cash Equivalents [Abstract]

Cash and Cash Equivalents, and Investment

Cash and Cash Equivalents, and Investments

The following tables shows our cash and cash equivalents, and investments’ adjusted cost, unrealized gain, unrealized loss and fair value as of September 30, 2019 and December 31, 2018 (in thousands):



	September 30, 2019
	Adjusted Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash and cash equivalents:
Cash	$	302,779	$	—	$	—		$	302,779
Money market funds	140,193		—		—			140,193
Commercial paper	7,496		—		(11		)	7,485
Total cash and cash equivalents	$	450,468	$	—	$	(11	)	$	450,457
Short-term investments:
Commercial paper	$	48,198	$	6	$	(1	)	$	48,203
Corporate securities	232,803		321		(82		)	233,042
U.S. treasury securities	39,095		44		—			39,139
Agency bonds	25,001		7		—			25,008
Total short-term investments	$	345,097	$	378	$	(83	)	$	345,392
Long-term investments:
Corporate securities	$	309,989	$	524	$	(366	)	$	310,147
Agency bonds	30,000		—		(29		)	29,971
Total long-term investments	$	339,989	$	524	$	(395	)	$	340,118



	December 31, 2018
	Adjusted Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash and cash equivalents:
Cash	$	351,345	$	—	$	—		$	351,345
Money market funds	5,052		—		—			5,052
Commercial paper	18,267		—		—			18,267
Total cash and cash equivalents	$	374,664	$	—	$	—		$	374,664
Short-term investments:
Commercial paper	$	40,500	$	—	$	(12	)	$	40,488
Corporate securities	38,616		—		(87		)	38,529
U.S. treasury securities	14,333		—		(5		)	14,328
Total short-term investments	$	93,449	$	—	$	(104	)	$	93,345
Long-term investments:
Corporate securities	$	14,429	$	9	$	(14	)	$	14,424
U.S. treasury securities	1,630		—		(2		)	1,628
Total long-term investments	$	16,059	$	9	$	(16	)	$	16,052

The adjusted cost and fair value of available-for-sale investments as of September 30, 2019 by contractual maturity were as follows (in thousands):



	Adjusted Cost		Fair Value
Due in 1 year or less	$	352,593	$	352,877
Due in 1-2 years	339,989		340,118
Investments not due at a single maturity date	140,193		140,193
Total	$	832,775	$	833,188

Investments not due at a single maturity date in the preceding table consist of money market fund deposits.

As of September 30, 2019, we considered the declines in market value of our investment portfolio to be temporary in nature and did not consider any of our investments to be other-than-temporarily impaired. We typically invest in highly-rated securities with a minimum credit rating of A- and a weighted average maturity of 10 months, and our investment policy generally limits the amount of credit exposure to any one issuer or industry sector. The policy requires investments generally to be investment grade, with the primary objective of preserving capital and maintaining liquidity. Fair values were determined for each individual security in the investment portfolio. When evaluating an investment for other-than-temporary impairment, we review factors such as the length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer and any changes thereto, changes in market interest rates and our intent to sell, or whether it is more likely than not it will be required to sell, the investment before recovery of the investment’s cost basis. During the three and nine months ended September 30, 2019 and 2018, we did not recognize any other-than-impairment charges.

Restricted Cash

As of September 30, 2019 and December 31, 2018, we had approximately $1.3 million of restricted cash that primarily consists of security deposits for our corporate offices. These amounts are classified in either other current assets or other assets on our condensed consolidated balance sheets based upon the term of the remaining restrictions.

Strategic Investments

In October 2018, we completed an investment of $10.0 million in WayUp, Inc., a U.S.-based job site and mobile application for college students and recent graduates. Additionally, we previously invested $3.0 million in a foreign entity to explore expanding our reach internationally. We did not record other-than-temporary impairment charges on our strategic investments during the three and nine months ended September 30, 2019 and 2018, as there were no significant identified events or changes in circumstances that would be considered an indicator for impairment. There were no observable price changes in orderly transactions for the identical or similar investments of the same issuer during the three and nine months ended September 30, 2019 and 2018.

Fair Value Measurement

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurement

We have established a fair value hierarchy used to determine the fair value of our financial instruments as follows:

Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities.

Level 2—Inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the assets or liabilities, either directly or indirectly through market corroboration, for substantially the full term of the financial instruments.

Level 3—Inputs are unobservable inputs based on our own assumptions used to measure assets and liabilities at fair value; the inputs require significant management judgment or estimation.

A financial instrument’s classification within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Financial instruments measured and recorded at fair value on a recurring basis as of September 30, 2019 and December 31, 2018 are classified based on the valuation technique level in the tables below (in thousands):



	September 30, 2019
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents:
Money market funds	$	140,193	$	140,193	$	—
Commercial paper	7,485		—		7,485
Short-term investments:
Commercial paper	48,203		—		48,203
Corporate securities	233,042		—		233,042
U.S. treasury securities	39,139		39,139		—
Agency bonds	25,008		—		25,008
Long-term investments:
Corporate securities	310,147		—		310,147
Agency bonds	29,971		—		29,971
Total assets measured and recorded at fair value	$	833,188	$	179,332	$	653,856



	December 31, 2018
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents:
Money market funds	$	5,052	$	5,052	$	—
Commercial paper	18,267		—		18,267
Short-term investments:
Commercial paper	40,488		—		40,488
Corporate securities	38,529		—		38,529
U.S. treasury securities	14,328		14,328		—
Long-term investments:
Corporate securities	14,424		—		14,424
U.S. treasury securities	1,628		1,628		—
Total assets measured and recorded at fair value	$	132,716	$	21,008	$	111,708

We value our investments based on quoted prices in active markets for identical assets (Level 1 inputs) or inputs other than quoted prices that are observable either directly or indirectly (Level 2 inputs) in determining fair value. Other than our money market funds and U.S. treasury securities, we classify our fixed income available-for-sale securities as having Level 2 inputs. The valuation techniques used to measure the fair value of our financial instruments having Level 2 inputs were derived from non-binding market consensus prices that are corroborated by observable market data, quoted market prices for similar instruments, or pricing models such as discounted cash flow techniques. We do not hold any investments valued with a Level 3 input.

The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while we believe our valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

Financial Instruments Not Recorded at Fair Value on a Recurring Basis

We report our financial instruments at fair value with the exception of the notes. The estimated fair value of the notes was determined based on the trading price of the notes as of the last day of trading for the period. We consider the fair value of the notes to be a Level 2 measurement due to the limited trading activity. For further information on the notes see Note 7, Convertible Senior Notes.

The carrying amounts and estimated fair values of the notes as of September 30, 2019 and December 31, 2018 are as follows (in thousands):



	September 30, 2019				December 31, 2018
	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
2025 notes	$	593,058	$	735,584	$	—	$	—
2023 notes	294,157		443,918		283,668		416,156
Convertible senior notes, net	$	887,215	$	1,179,502	$	283,668	$	416,156

The carrying amount of the 2025 notes and 2023 notes as of September 30, 2019 was net of unamortized debt discount of $193.6 million and $45.4 million, respectively, and unamortized issuance costs of $13.3 million and $5.4 million, respectively. The carrying amount of the 2023 notes as of December 31, 2018 was net of unamortized debt discount of $54.8 million and unamortized issuance costs of $6.5 million.

- 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

Goodwill and Intangible Assets

9 Months Ended

Sep. 30, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

Goodwill consists of the following (in thousands):



	Nine Months Ended September 30, 2019			Year Ended December 31, 2018
Beginning balance	$	149,524		$	125,272
Additions due to acquisitions	—			24,673
Foreign currency translation adjustment	(456		)	(421		)
Ending balance	$	149,068		$	149,524

Intangible assets as of September 30, 2019 and December 31, 2018 consist of the following (in thousands, except weighted-average amortization period):



	September 30, 2019
	Weighted-Average Amortization Period (in months)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Developed technologies and content library	71	$	31,667		$	(16,757	)	$	14,910
Customer lists	47	9,970			(7,872		)	2,098
Trade names	44	6,113			(5,681		)	432
Non-compete agreements	31	2,018			(1,865		)	153
Indefinite-lived trade name	—	3,600			—			3,600
Foreign currency translation adjustment	—	(571		)	—			(571		)
Total intangible assets	61	$	52,797		$	(32,175	)	$	20,622



	December 31, 2018
	Weighted-Average Amortization Period (in months)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Developed technologies and content library	71	$	31,667		$	(13,737	)	$	17,930
Customer lists	47	9,970			(6,847		)	3,123
Trade names	44	6,113			(4,863		)	1,250
Non-compete agreements	31	2,018			(1,735		)	283
Indefinite-lived trade name	—	3,600			—			3,600
Foreign currency translation adjustment	—	(271		)	—			(271		)
Total intangible assets	61	$	53,097		$	(27,182	)	$	25,915

During the three and nine months ended September 30, 2019, amortization expense related to our acquired intangible assets totaled approximately $1.5 million and $5.0 million, respectively. During the three and nine months ended September 30, 2018, amortization expense related to our acquired intangible assets totaled approximately $1.8 million and $4.7 million, respectively.

As of September 30, 2019, the estimated future amortization expense related to our finite-lived intangible assets is as follows (in thousands):



Remaining three months of 2019	$	1,455
2020	4,816
2021	3,423
2022	2,943
2023	2,276
Thereafter	2,109
Total	$	17,022

Convertible Senior Notes

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Convertible Senior Notes

In March 2019, we issued $700 million in aggregate principal amount of 0.125% convertible senior notes due in 2025 (2025 notes) and in April 2019, the initial purchasers fully exercised their option to purchase $100 million of additional notes for aggregate total principal amount of $800 million. In April 2018, we issued $345 million in aggregate principal amount of 0.25% convertible senior notes due in 2023 (2023 notes). The aggregate principal amount of the 2023 notes includes $45 million from the initial purchasers fully exercising their option to purchase additional notes. Collectively, the 2025 notes and 2023 notes are referred to as the “notes.” The notes were issued in private placements to qualified institutional buyers pursuant to Rule 144A of the Securities Act of 1933, as amended.

The total net proceeds from the notes are as follows (in thousands):



	2025 Notes			2023 Notes
Principal amount	$	800,000		$	345,000
Less initial purchasers’ discount	(18,998		)	(8,625		)
Less other issuance costs	(822		)	(757		)
Net proceeds	$	780,180		$	335,618

The notes are our senior, unsecured obligations and are governed by indenture agreements by and between us and Wells Fargo Bank, National Association, as Trustee (the indentures). The 2025 notes bear interest of 0.125% per year which is payable semi-annually in arrears on March 15 and September 15 of each year, beginning on September 15, 2019. The 2025 notes will mature on March 15, 2025 (the 2025 notes maturity date), unless repurchased, redeemed or converted in accordance with their terms prior to such date. The 2023 notes bear interest of 0.25% per year which is payable semi-annually in arrears on

May 15 and November 15 of each year, beginning on November 15, 2018. The 2023 notes will mature on May 15, 2023 (the 2023 notes maturity date), unless repurchased, redeemed or converted in accordance with their terms prior to such date.

Each $1,000 principal amount of the 2025 notes will initially be convertible into 19.3956 shares of our common stock. This is equivalent to an initial conversion price of approximately $51.56 per share, which is subject to adjustment in certain circumstances. Each $1,000 principal amount of the 2023 notes will initially be convertible into 37.1051 shares of our common stock. This is equivalent to an initial conversion price of approximately $26.95 per share, which is subject to adjustment in certain circumstances.

Prior to the close of business on the business day immediately preceding December 15, 2024 for the 2025 notes and February 15, 2023 for the 2023 notes, the notes are convertible at the option of holders only upon satisfaction of the following circumstances:

•

during any calendar quarter commencing after the calendar quarter ending on June 30, 2019 for the 2025 notes and June 30, 2018 for the 2023 notes, if the last reported sale price of our common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the respective conversion price for the notes on each applicable trading day;


•	during the five-business day period after any 10 consecutive trading day period (the measurement period) in which the trading price per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of our common stock and the conversion rate on each such trading day;


•	if we call any or all of the notes for redemption, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or


•	upon the occurrence of certain specified corporate events described in the indentures.

On or after December 15, 2024 for the 2025 notes and February 15, 2023 for the 2023 notes until the close of business on the second scheduled trading day immediately preceding the respective maturity dates, holders may convert their notes at any time, regardless of the foregoing circumstances. Upon conversion, the notes may be settled in shares of our common stock, cash or a combination of cash and shares of our common stock, at our election.

If we undergo a fundamental change, as defined in the indentures, prior to the respective maturity dates, subject to certain conditions, holders of the notes may require us to repurchase for cash all or any portion of their notes at a repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, if specific corporate events, described in the indentures, occur prior to the respective maturity dates, we will also increase the conversion rate for a holder who elects to convert their notes in connection with such specified corporate events.

During the three and nine months ended September 30, 2019, the conditions allowing holders of the 2025 notes to convert had not been met and were therefore not convertible. During the three and nine months ended September 30, 2019, the first circumstance allowing holders of the 2023 notes to convert had been met and are therefore convertible. None of the holders of the 2023 notes elected to convert their notes into shares of our common stock during the three and nine months ended September 30, 2019. During the three months ended September 30, 2018, the conditions allowing holders of the notes to convert had not been met and were therefore not convertible.

In accounting for the issuance of the notes, we separated the notes into liability and equity components. The carrying amount of the liability components for the 2025 notes and 2023 notes of approximately $588.0 million and $280.8 million, respectively, was calculated by measuring the fair value of similar debt instruments that do not have an associated convertible feature. The carrying amount of the equity components for the 2025 notes and 2023 notes of approximately $212.0 million and $64.2 million, respectively, representing the conversion option, was determined by deducting the carrying amount of the liability components from the principal amount of the notes. This difference between the principal amount of the notes and the liability components represents the debt discount, presented as a reduction to the notes on our condensed consolidated balance sheets, and is amortized to interest expense using the effective interest method over the remaining term of the notes. The equity components of the notes are included in additional paid-in capital on our condensed consolidated balance sheets and is not remeasured as long as it continues to meet the conditions for equity classification.

We incurred issuance costs related to the 2025 notes of approximately $19.8 million, consisting of the initial purchasers' discount of $19.0 million and other issuance costs of approximately $0.8 million. We incurred issuance costs related to the 2023 notes of approximately $9.4 million, consisting of the initial purchasers' discount of $8.6 million and other issuance costs of approximately $0.8 million. In accounting for the issuance costs, we allocated the total amount incurred to the liability and

equity components using the same proportions determined above for the notes. Transaction costs attributable to the liability components for the 2025 notes and 2023 notes of approximately $14.6 million and $7.6 million, respectively, were recorded as debt issuance cost, presented as a reduction to the notes on our condensed consolidated balance sheets, and are amortized to interest expense using the effective interest method over the term of the notes. The issuance costs attributable to the equity components for the 2025 notes and 2023 notes were approximately $5.3 million and $1.7 million, respectively, and were recorded as a reduction to the equity component included in additional paid-in capital.

The net carrying amount of the liability component of the notes is as follows (in thousands):



	September 30, 2019						December 31, 2018
	2025 Notes			2023 Notes			2023 Notes
Principal	$	800,000		$	345,000		$	345,000
Unamortized debt discount	(193,637		)	(45,440		)	(54,817		)
Unamortized issuance costs	(13,305		)	(5,403		)	(6,515		)
Net carrying amount (liability)	$	593,058		$	294,157		$	283,668

The net carrying amount of the equity component of the notes is as follows (in thousands):



	September 30, 2019						December 31, 2018
	2025 Notes			2023 Notes			2023 Notes
Debt discount for conversion option	$	212,000		$	64,193		$	64,193
Issuance costs	(5,253		)	(1,749		)	(1,749		)
Net carrying amount (equity)	$	206,747		$	62,444		$	62,444

As of September 30, 2019, the remaining lives of the 2025 notes and 2023 notes are approximately 5.5 and 3.6 years, respectively, and are classified as long-term debt.

Based on the closing price of our common stock of $29.95 on September 30, 2019, the if-converted value of the 2025 notes was approximately $464.7 million which is less than the principal amount of $800 million by approximately $335.3 million and the if-converted value of the 2023 notes was approximately $383.4 million which exceeds the principal amount of $345 million by approximately $38.4 million.

The effective interest rates of the liability components for the 2025 notes and 2023 notes are 5.40% and 4.34%, respectively, and each is based on the interest rate of similar debt instruments, at the time of our offering, that do not have associated convertible features. The following tables set forth the total interest expense recognized related to the notes (in thousands):



	Three Months Ended September 30,
	2019				2018
	2025 Notes		2023 Notes		2023 Notes
Contractual interest expense	$	252	$	217	$	218
Amortization of debt discount	8,939		3,161		3,160
Amortization of issuance costs	614		375		377
Total interest expense	$	9,805	$	3,753	$	3,755



	Nine Months Ended September 30,
	2019				2018
	2025 Notes		2023 Notes		2023 Notes
Contractual interest expense	$	517	$	645	$	428
Amortization of debt discount	18,363		9,377		6,217
Amortization of issuance costs	1,262		1,112		741
Total interest expense	$	20,142	$	11,134	$	7,386

Capped Call Transactions

Concurrently with the offering of the 2025 notes and 2023 notes, we used $97.2 million and $39.2 million, respectively, of the net proceeds to enter into privately negotiated capped call transactions which are expected to generally reduce or offset potential dilution to holders of our common stock upon conversion of the notes and/or offset the potential cash payments we would be required to make in excess of the principal amount of any converted notes. The capped call transactions automatically exercise upon conversion of the notes and cover 15,516,480 and 12,801,260 shares of our common stock for the 2025 notes and 2023 notes, respectively, and are intended to effectively increase the overall conversion price from $51.56 to $79.32 per share for the 2025 notes and $26.95 to $40.68 per share for the 2023 notes. The effective increase in conversion price as a result of the capped call transactions serves to reduce potential dilution to holders of our common stock and/or offset the cash payments we are required to make in excess of the principal amount of any converted notes. As these transactions meet certain accounting criteria, they are recorded in stockholders’ equity as a reduction of additional paid-in capital on our condensed consolidated balance sheets and are not accounted for as derivatives. The fair value of the capped call instrument is not remeasured each reporting period. The cost of the capped call is not expected to be deductible for tax purposes.

Impact to Earnings per Share

The notes will have no impact to diluted earnings per share until the average price of our common stock exceeds the conversion price for the 2025 notes and 2023 notes of $51.56 and $26.95 per share, respectively, because we intend to settle the principal amount of the notes in cash upon conversion. Under the treasury stock method, in periods we report net income, we are required to include the effect of additional shares that may be issued under the notes when the average price of our common stock exceeds each respective conversion price. However, as a result of the capped call transactions described above, there will be no economic dilution from the 2025 notes and 2023 notes up to $79.32 and $40.68, respectively, as exercise of the capped call instruments will reduce any dilution from the notes that would have otherwise occurred when the average price of our common stock exceeds the conversion price.

Leases

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

Leases

We have operating leases for corporate offices worldwide, which expire at various dates through 2024. Our primary operating lease commitments at September 30, 2019 are related to our corporate headquarters in Santa Clara, California. We have additional offices in California, Oregon, Georgia and New York in the United States and internationally in India, Israel and Germany. During the three months ended September 30, 2019, we reassessed the lease term for two of our leases in India resulting in $2.6 million of ROU assets obtained in exchange for operating lease liabilities.

As of September 30, 2019, we had operating lease ROU assets of $16.3 million and operating lease liabilities of $20.3 million. As of September 30, 2019, we do not have finance leases recorded on our condensed consolidated balance sheet. As of September 30, 2019, our weighted average remaining lease term was 4.0 years. During the three and nine months ended September 30, 2019, our weighted average discount rate was 4.7%.

Operating lease expense, net of immaterial sublease income, was approximately $1.2 million and $3.7 million during the three and nine months ended September 30, 2019, respectively. Variable lease cost was immaterial during the three and nine months ended September 30, 2019. We did not record short term lease cost during the three and nine months ended September 30, 2019.

The aggregate future minimum lease payments and reconciliation to lease liabilities as of September 30, 2019, are as follows (in thousands):



	September 30, 2019
Remaining three months of 2019	$	1,437
2020	5,834
2021	5,362
2022	5,147
2023	3,742
Thereafter	780
Total future minimum lease payments	22,302
Less imputed interest	(2,005		)
Total lease liabilities	$	20,297

The aggregate future minimum lease payments as of December 31, 2018, are as follows (in thousands):



	December 31, 2018
2019	$	5,222
2020	5,251
2021	4,775
2022	3,999
2023	3,421
Thereafter	788
Total	$	23,456

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies From time to time, third parties may assert patent infringement claims against us in the form of letters, litigation, or other forms of communication. In addition, we may from time to time be subject to other legal proceedings and claims in the ordinary course of business, including claims of alleged infringement of trademarks, copyrights, and other intellectual property rights; employment claims; and general contract or other claims. We may also, from time to time, be subject to various legal or government claims, disputes, or investigations. Such matters may include, but not be limited to, claims, disputes, or investigations related to warranty, refund, breach of contract, employment, intellectual property, government regulation, or compliance or other matters. On November 5, 2018, NetSoc, LLC filed a complaint in the U.S. District Court for the Southern District of New York for patent infringement against Chegg alleging that the Chegg Tutors service infringes U.S. Patent No. 9.978,107 and seeking unspecified compensatory damages. The patent was deemed invalid in a different litigation in July 2019. In August 2019, Chegg filed a motion seeking dismissal of this complaint based on the finding that the patent-in-suit is invalid. The motion is currently pending before the court. We have not recorded any amounts related to the above matter, as we do not believe that a loss is probable. We are not aware of any other pending legal matters or claims, individually or in the aggregate, that are expected to have a material adverse impact on our condensed consolidated financial position, results of operations or cash flows. However, our analysis of whether a claim may proceed to litigation cannot be predicted with certainty, nor can the results of litigation be predicted with certainty. Nevertheless, defending any of these actions, regardless of the outcome, may be costly, time consuming, distract management personnel and have a negative effect on our business. An adverse outcome in this action, including a judgment or settlement, may cause a material adverse effect on our future business, operating results and/or financial condition.

Guarantees and Indemnifications	9 Months Ended
Guarantees and Indemnifications	Sep. 30, 2019
Guarantees And Indemnifications [Abstract]
Guarantees and Indemnifications	Guarantees and Indemnifications We have agreed to indemnify our directors and officers for certain events or occurrences, subject to certain limits, while such persons are or were serving at our request in such capacity. We may terminate the indemnification agreements with these persons upon termination of employment, but termination will not affect claims for indemnification related to events occurring prior to the effective date of termination. We have a directors’ and officers’ insurance policy that limits our potential exposure up to the limits of our insurance coverage. In addition, we also have other indemnification agreements with various vendors against certain claims, liabilities, losses, and damages. The maximum amount of potential future indemnification is unlimited. We believe the fair value of these indemnification agreements is minimal. We have not recorded any liabilities for these agreements as of September 30, 2019.

Stockholders' Equity

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

Stockholders' Equity

In conjunction with our 2025 notes offering in March 2019, we repurchased 504,286 shares of our common stock at an average price per share of $39.66.

Share-based Compensation Expense

Total share-based compensation expense recorded for employees and non-employees is as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of revenues	$	96	$	106	$	295	$	303
Research and development	5,741		4,528		15,876		12,190
Sales and marketing	1,843		1,675		5,405		4,994
General and administrative	9,185		7,509		25,779		20,016
Total share-based compensation expense	$	16,865	$	13,818	$	47,355	$	37,503

RSU and PSU Activity

Activity for RSUs and PSUs is as follows:



	RSUs and PSUs Outstanding
	Shares Outstanding		Weighted Average Grant Date Fair Value
Balance at December 31, 2018	10,804,808		$	11.87
Granted	1,972,614		39.56
Released	(5,343,183	)	9.94
Canceled	(1,069,392	)	10.65
Balance at September 30, 2019	6,364,847		$	22.28

As of September 30, 2019, our total unrecognized share-based compensation expense related to RSUs and PSUs was approximately $84.2 million, which will be recognized over the remaining weighted-average vesting period of approximately 1.6 years.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We recorded an income tax provision of approximately $0.6 million and $1.8 million during the three and nine months ended September 30, 2019, respectively, primarily due to state and foreign income tax expense. We recorded an income tax provision of approximately $0.7 million and $1.7 million during the three and nine months ended September 30, 2018, respectively, primarily due to foreign and state tax expense offset by federal and state tax benefits related to deferred tax liabilities of acquired intangible assets.

Restructuring Charges

9 Months Ended

Sep. 30, 2019

Restructuring and Related Activities [Abstract]

Restructuring Charges

2017 Restructuring Plan

In January 2017, we entered into a strategic partnership with the National Research Center for College & University Admissions (NRCCUA) where they assumed responsibility for managing, renewing, and maintaining our existing university contracts and became the exclusive reseller of our digital marketing services for colleges and universities. As a result of this strategic partnership, approximately 55 employees in China and the United States supporting the sales and account support functions of our marketing services offerings were terminated. Costs incurred to date are expected to be fully paid within five months.

2015 Restructuring Plan

We recorded a reduction of $0.3 million to our 2015 Restructuring Plan liability related to our adoption of ASU 2016-02, Leases (Topic 842) during the three months ended March 31, 2019. Our 2015 Restructuring Plan is now complete.

The following table summarizes the activity related to the accrual for restructuring charges (in thousands):



	2017 Restructuring Plan						2015 Restructuring Plan
	Workforce Reduction Costs			Lease Termination and Other Costs			Lease Termination and Other Costs			Total
Balance at January 1, 2018	$	44		$	—		$	221		$	265
Restructuring charges	253			19			317			589
Cash payments	(151		)	(19		)	(218		)	(388		)
Write-offs	—			—			(18		)	(18		)
Balance at December 31, 2018	146			—			302			448
Cumulative-effect adjustment to accumulated deficit related to adoption of ASU 2016-02	—			—			(302		)	(302		)
Restructuring charges	97			—			—			97
Cash payments	(200		)	—			—			(200		)
Balance at September 30, 2019	$	43		$	—		$	—		$	43

Related-Party Transactions	9 Months Ended
Related-Party Transactions	Sep. 30, 2019
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions Our Chief Executive Officer is a member of the Board of Directors of Adobe Systems Incorporated (Adobe). During the three and nine months ended September 30, 2019, we had purchases of $0.4 million and $1.9 million, respectively, and during the three and nine months ended September 30, 2018, we had purchases of $0.6 million and $2.8 million, respectively, from Adobe. We had no revenues during the three and nine months ended September 30, 2019 from Adobe. We had no revenues during the three months ended September 30, 2018 and $0.1 million of revenues during the nine months ended September 30, 2018 from Adobe. We had an immaterial amount of payables as of September 30, 2019 and December 31, 2018 to Adobe. We had no outstanding receivables as of September 30, 2019 and December 31, 2018 from Adobe. One of our board members is also a member of the Board of Directors of Cengage Learning, Inc. (Cengage). During the three and nine months ended September 30, 2019, we had purchases of $4.2 million and $14.8 million, respectively, and during the three and nine months ended September 30, 2018, we had purchases of $3.8 million and $10.3 million, respectively, from Cengage. We had $1.3 million and $2.9 million of revenues during the three and nine months ended September 30, 2019, respectively, and $1.2 million and $3.2 million of revenues during the three and nine months ended September 30, 2018, respectively, from Cengage. We had an immaterial amount and $0.1 million in payables as of September 30, 2019 and December 31, 2018, respectively, to Cengage. We had an immaterial amount of outstanding receivables as of September 30, 2019 and December 31, 2018 from Cengage. The immediate family of one of our board members is also a member of the Board of Directors of PayPal Holdings, Inc. (PayPal). During the three and nine months ended September 30, 2019, we incurred payment processing fees of $0.4 million and $1.2 million, respectively, and during the three and nine months ended September 30, 2018, we incurred processing fees of $0.4 million and $1.0 million, respectively, to PayPal. One of our board members is also a member of the Board of Directors of Synack, Inc. (Synack). During the three and nine months ended September 30, 2019, we had purchases of $0.1 million and $0.4 million, respectively, for services from Synack.

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Acquisition of Thinkful, Inc. On October 1, 2019, we completed our acquisition of Thinkful, Inc. (Thinkful), a privately held online learning platform that offers professional courses directly to students across America. We acquired Thinkful for approximately $80.0 million in an all-cash transaction. There are potential additional payments of up to $20.0 million, which may be paid in cash or restricted stock units, at Chegg’s sole discretion, subject to performance-based contingencies. The initial accounting for this acquisition is in process as of the issuance date for our financial statements and therefore we are unable to make any additional disclosures. FedEx Supply Chain, Inc. (FedEx) Strategic Logistics Agreement On October 7, 2019, we signed a strategic logistics agreement with FedEx to provide logistics and warehousing services. The agreement begins on December 1, 2019 and continues through March 31, 2025 and the total fixed commitments are approximately $15.4 million.

Background and Basis of Presentation (Policies)	9 Months Ended
Background and Basis of Presentation (Policies)	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated balance sheet as of September 30, 2019, the condensed consolidated statements of operations, the condensed consolidated statements of comprehensive loss, and the condensed consolidated statements of stockholder's equity for the three and nine months ended September 30, 2019 and 2018, the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018 and the related footnote disclosures are unaudited. In the opinion of management, the accompanying unaudited condensed consolidated financial statements contain all adjustments, including normal recurring adjustments, necessary to present fairly our financial position as of September 30, 2019, our results of operations, results of comprehensive loss, and stockholder's equity for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018. Our results of operations, stockholder's equity, and cash flows for the nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the full year. We operate in a single segment. Our fiscal year ends on December 31 and in this report we refer to the year ended December 31, 2018 as 2018. The condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto that are included in our Annual Report on Form 10-K for the year ended December 31, 2018 (the Annual Report on Form 10-K) filed with the U.S. Securities and Exchange Commission (SEC). We have changed the captions on our condensed consolidated statements of cash flows from “purchases of marketable securities” to “purchases of investments” and from “maturities of marketable securities” to “maturities of investments.” This change does not impact any current or previously reported results. Except for our policies on leases and convertible senior notes, there have been no material changes to our significant accounting policies as compared to the significant accounting policies described in our Annual Report on Form 10-K.
Leases	Leases We determine if an arrangement is a lease at inception. Operating leases are included in operating lease right of use (ROU) assets, operating lease liabilities within current liabilities, and operating lease liabilities within long-term liabilities on our condensed consolidated balance sheet. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. Our leases do not provide an implicit rate and therefore we use our incremental borrowing rate based on the information available at commencement date in determining the present value of future minimum lease payments. Our incremental borrowing rate is estimated based on the estimated rate incurred to borrow, on a collateralized basis over a similar term as our leases, an amount equal to the lease payments in a similar economic environment. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise such options. We do not record leases on our condensed consolidated balance sheet with a term of one year or less. We do not separate lease and non-lease components but rather account for each separate component as a single lease component for all underlying classes of assets. Some of our leases include payments that are dependent on an index, such as the Consumer Price Index (CPI), and our minimum lease payments include payments based on the index at inception with any future changes in such indices recognized as an expense in the period of change. Where leases contain escalation clauses, rent abatements, or concessions, such as rent holidays and landlord or tenant incentives or allowances, we apply them in the determination of straight-line operating lease cost over the lease term.
Convertible Senior Notes, net	Convertible Senior Notes, net In March 2019, we issued $700 million in aggregate principal amount of 0.125% convertible senior notes due in 2025 (2025 notes) and in April 2019, the initial purchasers fully exercised their option to purchase $100 million of additional 2025 notes for aggregate total gross proceeds of $800 million. In April 2018, we issued $345 million in aggregate principal amount of 0.25% convertible senior notes due in 2023 (2023 notes). Collectively, the 2025 notes and the 2023 notes are referred to as the “notes.” In accounting for their issuance, we separated the notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of similar liabilities that do not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was determined by deducting the carrying amount of the liability component from the par value of the notes. The difference represents the debt discount, recorded as a reduction of the convertible senior notes on our condensed consolidated balance sheets, and is amortized to interest expense over the term of the notes using the effective interest rate method. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. In accounting for the issuance costs related to the notes, we allocated the total amount of issuance costs incurred to liability and equity components based on their relative values. Issuance costs attributable to the liability component are being amortized on a straight-line basis, which approximates the effective interest rate method, to interest expense over the term of the notes. The issuance costs attributable to the equity component are recorded as a reduction of the equity component within additional paid-in capital.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States (U.S. GAAP) requires management to make estimates, judgments, and assumptions that affect the reported amounts of assets and liabilities; the disclosure of contingent liabilities at the date of the financial statements; and the reported amounts of revenues and expenses during the reporting periods. Significant estimates, assumptions, and judgments are used for, but not limited to: revenue recognition, recoverability of accounts receivable, restructuring charges, share-based compensation expense including estimated forfeitures, accounting for income taxes, useful lives assigned to long-lived assets for depreciation and amortization, impairment of goodwill and long-lived assets, the valuation of acquired intangible assets, the valuation of our convertible senior notes, and operating lease ROU assets and operating lease liabilities. We base our estimates on historical experience, knowledge of current business conditions, and various other factors we believe to be reasonable under the circumstances. These estimates are based on management’s knowledge about current events and expectations about actions we may undertake in the future. Actual results could differ from these estimates, and such differences could be material to our financial position and results of operations.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Issued Accounting Pronouncements Not Yet Adopted In May 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief. ASU 2019-05 provides entities with an option to irrevocably elect the fair value option for eligible instruments. 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. ASU 2019-04 provides codification updates to ASU 2016-01 and ASU 2016-13. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. ASU 2016-13 replaces the existing incurred loss impairment model for trade receivables with an expected loss model which requires the use of forward-looking information to calculate expected credit loss estimates. Additionally, the concept of other-than-temporary impairment for available-for-sale investments is eliminated and instead ASU 2016-13 requires an entity to focus on determining whether any impairment is a result of a credit loss or other factors. It also requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction to the amortized cost basis. These changes may result in earlier recognition of credit losses. Early adoption is permitted and these guidance updates require a modified retrospective method of adoption, though a prospective method of adoption is required for available-for-sale debt securities for which an other-than-temporary impairment had been recognized before the effective date. These guidance updates are effective for annual periods beginning after December 15, 2019. We plan to adopt this guidance on January 1, 2020 and we are currently in the process of evaluating the impact of these guidance updates. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with existing guidance contained within subtopic 350-40 to develop or obtain internal-use software. Early adoption is permitted and the guidance allows for a retrospective or prospective application. The guidance is effective for annual periods beginning after December 15, 2019. We plan to adopt this guidance on January 1, 2020 under the prospective application and we are currently in the process of evaluating the impact of this guidance. In July 2018, the FASB issued ASU 2018-09, Codification Improvements. ASU 2018-09 provides updates for technical corrections, clarifications, and other minor improvements to a wide variety of topics in the ASC. The transition method of adoption is dependent on the ASC topic impacted by this guidance. Additionally, some of the ASC topic updates are effective upon issuance of ASU 2018-09 and some of the ASC topic updates are effective at a future date. The ASC topic updates effective upon issuance of ASU 2018-09 do not impact our accounting for the respective ASC topics. For those ASC topic updates effective at a future date, we are currently in the process of evaluating the impact of this guidance update. Recently Adopted Accounting Pronouncements The FASB has issued four ASUs related to Accounting Standards Codification (ASC) 842. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements and ASU 2018-10, Codification Improvements to Topic 842, Leases. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASC 842 requires an entity to recognize a ROU asset and lease liability for all leases with terms of more than 12 months. Recognition, measurement, and presentation of expenses will depend on classification as a finance or operating lease. The amendments in this update also require certain quantitative and qualitative disclosures about leasing arrangements. We have adopted ASC 842 on January 1, 2019 and have elected the transition method of adoption that allows for a modified retrospective adoption with a cumulative-effect adjustment to the opening balance of accumulated deficit and recorded an immaterial decrease to our opening balance of accumulated deficit. As a result, we have not changed previously disclosed amounts or provided additional disclosures for comparative periods. We initially recorded ROU assets of $17.2 million and lease liabilities of $21.1 million on our condensed consolidated balance sheet. ASC 842 does not have a material impact to our condensed consolidated statements of operations. We have elected a package of transition practical expedients which include not reassessing whether any expired or existing contracts are or contain leases, not reassessing the lease classification of expired or existing leases, and not reassessing initial direct costs for existing leases. We have also elected a practical expedient to not separate lease and non-lease components. We did not elect the practical expedient to use hindsight in determining our lease terms or assessing impairment of our ROU assets. See Note 8. Leases for more information.
Revenue Recognition	Revenue Recognition Revenues are recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. The majority of our revenues are recognized over time as services are performed, with certain revenues, most significantly the revenue share we earn from our print textbook partners, being recognized at the point in time when print textbooks are shipped to students.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential shares of common stock, including stock options, restricted stock units (RSUs), performance-based restricted stock units (PSUs), and shares related to convertible senior notes, to the extent dilutive. Basic and diluted net loss per share was the same for each period presented as the inclusion of all potential common shares outstanding would have been anti-dilutive.

Revenues (Tables)

9 Months Ended

Sep. 30, 2019

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following tables set forth our total net revenues for the periods shown disaggregated for our Chegg Services and Required Materials product lines (in thousands, except percentages):



	Three Months Ended September 30,				Change
	2019		2018		$		%
Chegg Services	$	69,304	$	54,201	$	15,103	28	%
Required Materials	24,847		20,036		4,811		24
Total net revenues	$	94,151	$	74,237	$	19,914	27



	Nine Months Ended September 30,				Change
	2019		2018		$		%
Chegg Services	$	224,903	$	172,327	$	52,576	31	%
Required Materials	60,519		53,081		7,438		14
Total net revenues	$	285,422	$	225,408	$	60,014	27

Schedule of Accounts Receivable

The following table presents our accounts receivable, net and deferred revenue balances (in thousands, except percentages):



					Change
	September 30, 2019		December 31, 2018		$		%
Accounts receivable, net	$	13,678	$	12,733	$	945	7	%
Deferred revenue	$	27,457	$	17,418	$	10,039	58	%

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2019

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The following table sets forth the computation of basic and diluted net loss per share (in thousands, except per share amounts):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2019			2018			2019			2018
Numerator:
Net loss	$	(11,477	)	$	(13,709	)	$	(17,824	)	$	(20,235	)
Denominator:
Weighted average shares used to compute net loss per share, basic and diluted	120,085			114,184			118,547			112,621

Net loss per share, basic and diluted	$	(0.10	)	$	(0.12	)	$	(0.15	)	$	(0.18	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following potential weighted-average shares of common stock outstanding were excluded from the computation of diluted net loss per share because including them would have been anti-dilutive (in thousands):



	Three Months Ended September 30,		Nine Months Ended September 30,
	2019	2018	2019	2018
Options to purchase common stock	2,122	3,961	2,715	4,282
RSUs and PSUs	3,831	7,479	4,952	8,075
Shares related to convertible senior notes	4,098	1,221	3,709	—
Employee stock purchase plan	7	17	3	12
Total common stock equivalents	10,058	12,678	11,379	12,369

Cash and Cash Equivalents, and Investment (Tables)

9 Months Ended

Sep. 30, 2019

Cash and Cash Equivalents [Abstract]

Cash, Cash Equivalents and Investments

The following tables shows our cash and cash equivalents, and investments’ adjusted cost, unrealized gain, unrealized loss and fair value as of September 30, 2019 and December 31, 2018 (in thousands):



	September 30, 2019
	Adjusted Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash and cash equivalents:
Cash	$	302,779	$	—	$	—		$	302,779
Money market funds	140,193		—		—			140,193
Commercial paper	7,496		—		(11		)	7,485
Total cash and cash equivalents	$	450,468	$	—	$	(11	)	$	450,457
Short-term investments:
Commercial paper	$	48,198	$	6	$	(1	)	$	48,203
Corporate securities	232,803		321		(82		)	233,042
U.S. treasury securities	39,095		44		—			39,139
Agency bonds	25,001		7		—			25,008
Total short-term investments	$	345,097	$	378	$	(83	)	$	345,392
Long-term investments:
Corporate securities	$	309,989	$	524	$	(366	)	$	310,147
Agency bonds	30,000		—		(29		)	29,971
Total long-term investments	$	339,989	$	524	$	(395	)	$	340,118



	December 31, 2018
	Adjusted Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash and cash equivalents:
Cash	$	351,345	$	—	$	—		$	351,345
Money market funds	5,052		—		—			5,052
Commercial paper	18,267		—		—			18,267
Total cash and cash equivalents	$	374,664	$	—	$	—		$	374,664
Short-term investments:
Commercial paper	$	40,500	$	—	$	(12	)	$	40,488
Corporate securities	38,616		—		(87		)	38,529
U.S. treasury securities	14,333		—		(5		)	14,328
Total short-term investments	$	93,449	$	—	$	(104	)	$	93,345
Long-term investments:
Corporate securities	$	14,429	$	9	$	(14	)	$	14,424
U.S. treasury securities	1,630		—		(2		)	1,628
Total long-term investments	$	16,059	$	9	$	(16	)	$	16,052

Schedule of Available-for-sale Securities Reconciliation

The adjusted cost and fair value of available-for-sale investments as of September 30, 2019 by contractual maturity were as follows (in thousands):



	Adjusted Cost		Fair Value
Due in 1 year or less	$	352,593	$	352,877
Due in 1-2 years	339,989		340,118
Investments not due at a single maturity date	140,193		140,193
Total	$	832,775	$	833,188

Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

Financial instruments measured and recorded at fair value on a recurring basis as of September 30, 2019 and December 31, 2018 are classified based on the valuation technique level in the tables below (in thousands):



	September 30, 2019
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents:
Money market funds	$	140,193	$	140,193	$	—
Commercial paper	7,485		—		7,485
Short-term investments:
Commercial paper	48,203		—		48,203
Corporate securities	233,042		—		233,042
U.S. treasury securities	39,139		39,139		—
Agency bonds	25,008		—		25,008
Long-term investments:
Corporate securities	310,147		—		310,147
Agency bonds	29,971		—		29,971
Total assets measured and recorded at fair value	$	833,188	$	179,332	$	653,856



	December 31, 2018
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents:
Money market funds	$	5,052	$	5,052	$	—
Commercial paper	18,267		—		18,267
Short-term investments:
Commercial paper	40,488		—		40,488
Corporate securities	38,529		—		38,529
U.S. treasury securities	14,328		14,328		—
Long-term investments:
Corporate securities	14,424		—		14,424
U.S. treasury securities	1,628		1,628		—
Total assets measured and recorded at fair value	$	132,716	$	21,008	$	111,708

Fair Value Measurements, Nonrecurring

The carrying amounts and estimated fair values of the notes as of September 30, 2019 and December 31, 2018 are as follows (in thousands):



	September 30, 2019				December 31, 2018
	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
2025 notes	$	593,058	$	735,584	$	—	$	—
2023 notes	294,157		443,918		283,668		416,156
Convertible senior notes, net	$	887,215	$	1,179,502	$	283,668	$	416,156

Goodwill and Intangible Assets (Tables)

9 Months Ended

Sep. 30, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Goodwill

Goodwill consists of the following (in thousands):



	Nine Months Ended September 30, 2019			Year Ended December 31, 2018
Beginning balance	$	149,524		$	125,272
Additions due to acquisitions	—			24,673
Foreign currency translation adjustment	(456		)	(421		)
Ending balance	$	149,068		$	149,524

Finite-Lived Intangible Assets

Intangible assets as of September 30, 2019 and December 31, 2018 consist of the following (in thousands, except weighted-average amortization period):



	September 30, 2019
	Weighted-Average Amortization Period (in months)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Developed technologies and content library	71	$	31,667		$	(16,757	)	$	14,910
Customer lists	47	9,970			(7,872		)	2,098
Trade names	44	6,113			(5,681		)	432
Non-compete agreements	31	2,018			(1,865		)	153
Indefinite-lived trade name	—	3,600			—			3,600
Foreign currency translation adjustment	—	(571		)	—			(571		)
Total intangible assets	61	$	52,797		$	(32,175	)	$	20,622



	December 31, 2018
	Weighted-Average Amortization Period (in months)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Developed technologies and content library	71	$	31,667		$	(13,737	)	$	17,930
Customer lists	47	9,970			(6,847		)	3,123
Trade names	44	6,113			(4,863		)	1,250
Non-compete agreements	31	2,018			(1,735		)	283
Indefinite-lived trade name	—	3,600			—			3,600
Foreign currency translation adjustment	—	(271		)	—			(271		)
Total intangible assets	61	$	53,097		$	(27,182	)	$	25,915

Indefinite-lived Intangible Assets

Intangible assets as of September 30, 2019 and December 31, 2018 consist of the following (in thousands, except weighted-average amortization period):



	September 30, 2019
	Weighted-Average Amortization Period (in months)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Developed technologies and content library	71	$	31,667		$	(16,757	)	$	14,910
Customer lists	47	9,970			(7,872		)	2,098
Trade names	44	6,113			(5,681		)	432
Non-compete agreements	31	2,018			(1,865		)	153
Indefinite-lived trade name	—	3,600			—			3,600
Foreign currency translation adjustment	—	(571		)	—			(571		)
Total intangible assets	61	$	52,797		$	(32,175	)	$	20,622



	December 31, 2018
	Weighted-Average Amortization Period (in months)	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Developed technologies and content library	71	$	31,667		$	(13,737	)	$	17,930
Customer lists	47	9,970			(6,847		)	3,123
Trade names	44	6,113			(4,863		)	1,250
Non-compete agreements	31	2,018			(1,735		)	283
Indefinite-lived trade name	—	3,600			—			3,600
Foreign currency translation adjustment	—	(271		)	—			(271		)
Total intangible assets	61	$	53,097		$	(27,182	)	$	25,915

Estimated Future Amortization Expense Related to Intangible Assets

As of September 30, 2019, the estimated future amortization expense related to our finite-lived intangible assets is as follows (in thousands):



Remaining three months of 2019	$	1,455
2020	4,816
2021	3,423
2022	2,943
2023	2,276
Thereafter	2,109
Total	$	17,022

Convertible Senior Notes (Tables)

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Schedule Of Net Proceeds From Debt Issuance

The total net proceeds from the notes are as follows (in thousands):



	2025 Notes			2023 Notes
Principal amount	$	800,000		$	345,000
Less initial purchasers’ discount	(18,998		)	(8,625		)
Less other issuance costs	(822		)	(757		)
Net proceeds	$	780,180		$	335,618

Schedule of Debt

The net carrying amount of the liability component of the notes is as follows (in thousands):



	September 30, 2019						December 31, 2018
	2025 Notes			2023 Notes			2023 Notes
Principal	$	800,000		$	345,000		$	345,000
Unamortized debt discount	(193,637		)	(45,440		)	(54,817		)
Unamortized issuance costs	(13,305		)	(5,403		)	(6,515		)
Net carrying amount (liability)	$	593,058		$	294,157		$	283,668

The net carrying amount of the equity component of the notes is as follows (in thousands):



	September 30, 2019						December 31, 2018
	2025 Notes			2023 Notes			2023 Notes
Debt discount for conversion option	$	212,000		$	64,193		$	64,193
Issuance costs	(5,253		)	(1,749		)	(1,749		)
Net carrying amount (equity)	$	206,747		$	62,444		$	62,444

Schedule Of Interest Expense Recognized

The following tables set forth the total interest expense recognized related to the notes (in thousands):



	Three Months Ended September 30,
	2019				2018
	2025 Notes		2023 Notes		2023 Notes
Contractual interest expense	$	252	$	217	$	218
Amortization of debt discount	8,939		3,161		3,160
Amortization of issuance costs	614		375		377
Total interest expense	$	9,805	$	3,753	$	3,755



	Nine Months Ended September 30,
	2019				2018
	2025 Notes		2023 Notes		2023 Notes
Contractual interest expense	$	517	$	645	$	428
Amortization of debt discount	18,363		9,377		6,217
Amortization of issuance costs	1,262		1,112		741
Total interest expense	$	20,142	$	11,134	$	7,386

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Leases (Tables)

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

Lessee, Operating Lease, Liability, Maturity

The aggregate future minimum lease payments and reconciliation to lease liabilities as of September 30, 2019, are as follows (in thousands):



	September 30, 2019
Remaining three months of 2019	$	1,437
2020	5,834
2021	5,362
2022	5,147
2023	3,742
Thereafter	780
Total future minimum lease payments	22,302
Less imputed interest	(2,005		)
Total lease liabilities	$	20,297

Schedule of Property Subject to or Available for Operating Lease

The aggregate future minimum lease payments as of December 31, 2018, are as follows (in thousands):



	December 31, 2018
2019	$	5,222
2020	5,251
2021	4,775
2022	3,999
2023	3,421
Thereafter	788
Total	$	23,456

Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation Expense for Employees and Non-Employees

Total share-based compensation expense recorded for employees and non-employees is as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of revenues	$	96	$	106	$	295	$	303
Research and development	5,741		4,528		15,876		12,190
Sales and marketing	1,843		1,675		5,405		4,994
General and administrative	9,185		7,509		25,779		20,016
Total share-based compensation expense	$	16,865	$	13,818	$	47,355	$	37,503

Summary of Restricted Stock Unit Activity

Activity for RSUs and PSUs is as follows:



	RSUs and PSUs Outstanding
	Shares Outstanding		Weighted Average Grant Date Fair Value
Balance at December 31, 2018	10,804,808		$	11.87
Granted	1,972,614		39.56
Released	(5,343,183	)	9.94
Canceled	(1,069,392	)	10.65
Balance at September 30, 2019	6,364,847		$	22.28

Restructuring Charges (Tables)

9 Months Ended

Sep. 30, 2019

Restructuring and Related Activities [Abstract]

Schedule of Restructuring Reserve by Type of Cost

The following table summarizes the activity related to the accrual for restructuring charges (in thousands):



	2017 Restructuring Plan						2015 Restructuring Plan
	Workforce Reduction Costs			Lease Termination and Other Costs			Lease Termination and Other Costs			Total
Balance at January 1, 2018	$	44		$	—		$	221		$	265
Restructuring charges	253			19			317			589
Cash payments	(151		)	(19		)	(218		)	(388		)
Write-offs	—			—			(18		)	(18		)
Balance at December 31, 2018	146			—			302			448
Cumulative-effect adjustment to accumulated deficit related to adoption of ASU 2016-02	—			—			(302		)	(302		)
Restructuring charges	97			—			—			97
Cash payments	(200		)	—			—			(200		)
Balance at September 30, 2019	$	43		$	—		$	—		$	43

Background and Basis of Presentation (Details) - USD ($)	1 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Sep. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Right of use assets			$ 16,312,000			$ 0
Operating lease liability			20,297,000
Senior Notes \| 0.125% Convertible Senior Notes Due 2025
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Face value	$ 100,000,000		800,000,000	$ 700,000,000
Interest rate, stated percentage				0.125%
Proceeds from issuance of debt	$ 800,000,000
Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Face value		$ 345,000,000	$ 345,000,000			$ 345,000,000
Interest rate, stated percentage		0.25%
Proceeds from issuance of debt		$ 345,000,000
Accounting Standards Update 2016-02
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Right of use assets					$ 17,200,000
Operating lease liability					$ 21,100,000

Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Revenues (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total net revenues	$ 94,151	$ 74,237	$ 285,422	$ 225,408
Change in total net revenues	$ 19,914		$ 60,014
Change in total net revenues, percent	27.00%		27.00%
Contract with customer, liability, revenue recognized	$ 15,700		$ 16,000
Contract with customer, liability, revenue recognized, prior period	2,200		2,700
Aggregate amount of unsatisfied performance obligations	29,000		29,000
Accounts receivable, net	13,678		13,678		$ 12,733
Change in accounts receivable			$ 945
Change in accounts receivable, percent			7.00%
Deferred Revenue, Period Increase (Decrease)			$ 10,000
Deferred revenue	27,457		27,457		$ 17,418
Change in deferred revenue			$ 10,039
Change in deferred revenue, percent			58.00%
Chegg Services
Disaggregation of Revenue [Line Items]
Total net revenues	69,304	54,201	$ 224,903	172,327
Change in total net revenues	$ 15,103		$ 52,576
Change in total net revenues, percent	28.00%		31.00%
Required Materials
Disaggregation of Revenue [Line Items]
Total net revenues	$ 24,847	$ 20,036	$ 60,519	$ 53,081
Change in total net revenues	$ 4,811		$ 7,438
Change in total net revenues, percent	24.00%		14.00%

Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss	$ (11,477)	$ (13,709)	$ (17,824)	$ (20,235)
Denominator:
Weighted average shares used to compute net loss per share, basic and diluted (in shares)	120,085	114,184	118,547	112,621
Net loss per share, basic and diluted (in dollars per share)	$ (0.10)	$ (0.12)	$ (0.15)	$ (0.18)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss Per Share - Shares Excluded From Computation Of Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Apr. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	10,058	12,678	11,379	12,369
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	2,122	3,961	2,715	4,282
RSUs and PSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	3,831	7,479	4,952	8,075
Shares related to convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	4,098	1,221	3,709	0
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	7	17	3	12
0.25% Convertible Senior Notes Due 2023 \| Shares related to convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Face value	$ 345,000,000		$ 345,000,000				$ 345,000,000	$ 345,000,000
Conversion price								$ 26.95
Interest rate, stated percentage								0.25%
0.125% Convertible Senior Notes Due 2025 \| Shares related to convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Face value	$ 800,000,000		$ 800,000,000		$ 100,000,000	$ 700,000,000
Conversion price	$ 51.56		$ 51.56
Interest rate, stated percentage						0.125%
Capped Call \| 0.25% Convertible Senior Notes Due 2023 \| Shares related to convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price	40.68		40.68
Capped Call \| 0.125% Convertible Senior Notes Due 2025 \| Shares related to convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price	$ 79.32		$ 79.32

Cash and Cash Equivalents, and Investment - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Oct. 31, 2018
Schedule of Investments [Line Items]
Weighted average maturity	10 months
Restricted cash	$ 1.3	$ 1.3
Cost method investment			$ 10.0
Other Assets \| Equity Investments
Schedule of Investments [Line Items]
Investments	$ 3.0

Cash and Cash Equivalents, and Investment - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 832,775
Fair Value	833,188
Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	450,468	$ 374,664
Unrealized Gain	0	0
Unrealized Loss	(11)	0
Fair Value	450,457	374,664
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	345,097	93,449
Unrealized Gain	378	0
Unrealized Loss	(83)	(104)
Fair Value	345,392	93,345
Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	339,989	16,059
Unrealized Gain	524	9
Unrealized Loss	(395)	(16)
Fair Value	340,118	16,052
Cash \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	302,779	351,345
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	302,779	351,345
Money market funds \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	140,193	5,052
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	140,193	5,052
Commercial paper \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	7,496	18,267
Unrealized Gain	0	0
Unrealized Loss	(11)	0
Fair Value	7,485	18,267
Commercial paper \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	48,198	40,500
Unrealized Gain	6	0
Unrealized Loss	(1)	(12)
Fair Value	48,203	40,488
Corporate securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	232,803	38,616
Unrealized Gain	321	0
Unrealized Loss	(82)	(87)
Fair Value	233,042	38,529
Corporate securities \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	309,989	14,429
Unrealized Gain	524	9
Unrealized Loss	(366)	(14)
Fair Value	310,147	14,424
U.S. treasury securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	39,095	14,333
Unrealized Gain	44	0
Unrealized Loss	0	(5)
Fair Value	39,139	14,328
U.S. treasury securities \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost		1,630
Unrealized Gain		0
Unrealized Loss		(2)
Fair Value		$ 1,628
Agency bonds \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	25,001
Unrealized Gain	7
Unrealized Loss	0
Fair Value	25,008
Agency bonds \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	30,000
Unrealized Gain	0
Unrealized Loss	(29)
Fair Value	$ 29,971

Cash and Cash Equivalents, and Investment - Contractual Maturity (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Cash and Cash Equivalents [Abstract]
Due in 1 year or less, Cost	$ 352,593
Due in 1-2 years, Cost	339,989
Investments not due at a single maturity date, Cost	140,193
Adjusted Cost	832,775
Due in 1 year or less, Fair Value	352,877
Due in 1-2 years, Fair Value	340,118
Investments not due at a single maturity date, Fair Value	140,193
Total, Fair Value	$ 833,188
Weighted average maturity	10 months

Fair Value Measurement - Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 345,392	$ 93,345
Long-term investments	340,118	16,052
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured and recorded at fair value	833,188	132,716
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured and recorded at fair value	179,332	21,008
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured and recorded at fair value	653,856	111,708
Commercial paper \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	48,203	40,488
Commercial paper \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Commercial paper \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	48,203	40,488
Corporate securities \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	233,042	38,529
Long-term investments	310,147	14,424
Corporate securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Long-term investments	0	0
Corporate securities \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	233,042	38,529
Long-term investments	310,147	14,424
U.S. treasury securities \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	39,139	14,328
Long-term investments		1,628
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	39,139	14,328
Long-term investments		1,628
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Long-term investments		0
Agency bonds \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	25,008
Long-term investments	29,971
Agency bonds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0
Long-term investments	0
Agency bonds \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	25,008
Long-term investments	29,971
Money market funds \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	140,193	5,052
Money market funds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	140,193	5,052
Money market funds \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Commercial paper \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	7,485	18,267
Commercial paper \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Commercial paper \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 7,485	$ 18,267

Fair Value Measurement - Debt (Details) - Senior Notes - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Carrying Amount \| Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes	$ 887,215	$ 283,668
Estimated Fair Value \| Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes	1,179,502	416,156
0.125% Convertible Senior Notes Due 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unamortized debt discount	193,637
Unamortized issuance costs	13,305
0.125% Convertible Senior Notes Due 2025 \| Carrying Amount \| Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes	593,058	0
0.125% Convertible Senior Notes Due 2025 \| Estimated Fair Value \| Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes	735,584	0
0.25% Convertible Senior Notes Due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unamortized debt discount	45,440	54,817
Unamortized issuance costs	5,403	6,515
0.25% Convertible Senior Notes Due 2023 \| Carrying Amount \| Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes	294,157	283,668
0.25% Convertible Senior Notes Due 2023 \| Estimated Fair Value \| Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes	$ 443,918	$ 416,156

Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning balance	$ 149,524	$ 125,272
Additions due to acquisitions	0	24,673
Foreign currency translation adjustment	(456)	(421)
Ending balance	$ 149,068	$ 149,524

Goodwill and Intangible Assets - Finite-lived and Indefinite-lived Intangibe Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period (in months)	61 months	61 months
Accumulated Amortization	$ (32,175)	$ (27,182)
Net Carrying Amount	17,022
Indefinite-lived trade name	3,600	3,600
Foreign currency translation adjustment	(571)	(271)
Total intangible assets, gross carrying amount	52,797	53,097
Intangible assets, net	$ 20,622	$ 25,915
Developed technologies and content library
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period (in months)	71 months	71 months
Gross Carrying Amount	$ 31,667	$ 31,667
Accumulated Amortization	(16,757)	(13,737)
Net Carrying Amount	$ 14,910	$ 17,930
Customer lists
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period (in months)	47 months	47 months
Gross Carrying Amount	$ 9,970	$ 9,970
Accumulated Amortization	(7,872)	(6,847)
Net Carrying Amount	$ 2,098	$ 3,123
Trade names
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period (in months)	44 months	44 months
Gross Carrying Amount	$ 6,113	$ 6,113
Accumulated Amortization	(5,681)	(4,863)
Net Carrying Amount	$ 432	$ 1,250
Non-compete agreements
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period (in months)	31 months	31 months
Gross Carrying Amount	$ 2,018	$ 2,018
Accumulated Amortization	(1,865)	(1,735)
Net Carrying Amount	$ 153	$ 283

Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Acquisition-Related Intangible Assets
Finite Lived Intangible Assets [Line Items]
Amortization expense of acquisition related to acquired intangible assets	$ 1.5	$ 1.8	$ 5.0	$ 4.7

Goodwill and Intangible Assets - Estimated Future Amortization Expense Related to Intangible Assets (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining three months of 2019	$ 1,455
2020	4,816
2021	3,423
2022	2,943
2023	2,276
Thereafter	2,109
Net Carrying Amount	$ 17,022

Convertible Senior Notes - Convertible Senior Notes (Details)	1 Months Ended			9 Months Ended
	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) shares	Apr. 30, 2018 USD ($) day $ / shares shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Net proceeds				$ 780,180,000	$ 335,618,000
Senior Notes \| 0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Face value	$ 100,000,000	$ 700,000,000		$ 800,000,000
Proceeds from issuance of debt	800,000,000
Interest rate, stated percentage		0.125%
Less initial purchasers’ discount	(18,998,000)
Less other issuance costs	(822,000)
Net proceeds	$ 780,180,000
Conversion price \| $ / shares				$ 51.56
Equity component				$ 206,747,000
Debt issuance costs				$ (19,800,000)
Debt instrument, remaining useful life				5 years 6 months
Debt conversion, converted instrument, amount				$ 464,700,000
Debt instrument, if-converted value less than principal				$ (335,300,000)
Interest rate, effective percentage				5.40%
Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Face value			$ 345,000,000	$ 345,000,000		$ 345,000,000
Proceeds from issuance of debt			$ 345,000,000
Interest rate, stated percentage			0.25%
Option to purchase additional notes			$ 45,000,000
Less initial purchasers’ discount			(8,625,000)
Less other issuance costs			(757,000)
Net proceeds			$ 335,618,000
Conversion ratio		0.0193956	0.0371051
Conversion price \| $ / shares			$ 26.95
Equity component			$ 64,200,000	$ 62,444,000		$ 62,444,000
Debt issuance costs			$ (9,400,000)
Debt instrument, remaining useful life				3 years 7 months 6 days
Share price (in dollars per share) \| $ / shares				$ 29.95
Debt conversion, converted instrument, amount				$ 383,400,000
Debt instrument, if-converted value in excess of principal				38,400,000
Interest rate, effective percentage			4.34%
Sale Price Is Greater Or Equal 130% \| Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Threshold trading days \| day			20
Threshold consecutive trading days \| day			30
Threshold percentage of stock price trigger			130.00%
Trading Price Per $1,000 Principal Amount Less Than 98% \| Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Threshold trading days \| day			5
Threshold consecutive trading days \| day			10
Trading Price Per $1,000 Principal Amount Less Than 98% \| Senior Notes \| 0.25% Convertible Senior Notes Due 2023 \| Maximum
Debt Instrument [Line Items]
Threshold percentage of stock price trigger			98.00%
Liability component \| Senior Notes \| 0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Net carrying amount				588,000,000.0
Equity component				212,000,000.0
Debt issuance costs				(14,600,000)
Liability component \| Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Net carrying amount			$ 280,800,000
Debt issuance costs			(7,600,000)
Equity component \| Senior Notes \| 0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Debt issuance costs				$ (5,300,000)
Equity component \| Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Debt issuance costs			(1,700,000)
Capped Call \| Senior Notes \| 0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Net proceeds		$ 97,200,000
Conversion price \| $ / shares				$ 79.32
Shares covered by capped call transactions (in shares) \| shares		15,516,480
Capped Call \| Senior Notes \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Net proceeds			$ 39,200,000
Conversion price \| $ / shares				$ 40.68
Shares covered by capped call transactions (in shares) \| shares			12,801,260

Convertible Senior Notes - Net Carrying Amount (Details) - Senior Notes - USD ($)	Sep. 30, 2019	Apr. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Apr. 30, 2018
0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Principal	$ 800,000,000	$ 100,000,000	$ 700,000,000
Unamortized debt discount	(193,637,000)
Unamortized issuance costs	(13,305,000)
Debt discount for conversion option	212,000,000
Issuance costs	(5,253,000)
Net carrying amount (equity)	206,747,000
0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Principal	345,000,000			$ 345,000,000	$ 345,000,000
Unamortized debt discount	(45,440,000)			(54,817,000)
Unamortized issuance costs	(5,403,000)			(6,515,000)
Debt discount for conversion option	64,193,000			64,193,000
Issuance costs	(1,749,000)			(1,749,000)
Net carrying amount (equity)	62,444,000			62,444,000	$ 64,200,000
Carrying Amount \| Fair Value, Measurements, Nonrecurring
Debt Instrument [Line Items]
Net carrying amount (liability)	887,215,000			283,668,000
Carrying Amount \| Fair Value, Measurements, Nonrecurring \| 0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Net carrying amount (liability)	593,058,000			0
Carrying Amount \| Fair Value, Measurements, Nonrecurring \| 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Net carrying amount (liability)	$ 294,157,000			$ 283,668,000

Convertible Senior Notes - Interest Expense Recognized (Details) - Senior Notes - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
0.125% Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Contractual interest expense	$ 252		$ 517
Amortization of debt discount	8,939		18,363
Amortization of issuance costs	614		1,262
Total interest expense	9,805		20,142
0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Contractual interest expense	217	$ 218	645	$ 428
Amortization of debt discount	3,161	3,160	9,377	6,217
Amortization of issuance costs	375	377	1,112	741
Total interest expense	$ 3,753	$ 3,755	$ 11,134	$ 7,386

Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Right of use assets	$ 16,312	$ 16,312	$ 0
Operating lease liability	$ 20,297	$ 20,297
Weighted average remaining lease term for operating lease	4 years	4 years
Weighted average discount rate used to determine the operating lease liability	4.70%	4.70%
Lease expense	$ 1,200	$ 3,700
INDIA
Lessee, Lease, Description [Line Items]
Right of use assets	2,600	2,600
Operating lease liability	$ 2,600	$ 2,600

Leases - Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Remaining three months of 2019	$ 1,437
2020	5,834
2021	5,362
2022	5,147
2023	3,742
2024	780
Total future minimum lease payments	22,302
Less imputed interest	(2,005)
Total lease liabilities	$ 20,297
2019		$ 5,222
2020		5,251
2021		4,775
2022		3,999
2023		3,421
Thereafter		788
Total		$ 23,456

Stockholders' Equity - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 16,865	$ 13,818	$ 47,355	$ 37,503
Cost of revenues
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	96	106	295	303
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	5,741	4,528	15,876	12,190
Sales and marketing
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,843	1,675	5,405	4,994
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 9,185	$ 7,509	$ 25,779	$ 20,016

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2019	Sep. 30, 2019
RSUs and PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs related to restricted stock units		$ 84.2
Weighted average vesting period for recognition of compensation expense		1 year 7 months 6 days
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares repurchased (in shares)	504,286
Share price (in dollars per share)		$ 39.66

Stockholders' Equity - Summary of Restricted Stock Unit Activity (Details) - RSUs and PSUs	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Shares Outstanding
Number of RSUs and PSUs Outstanding, Beginning (shares) \| shares	10,804,808
Number of RSUs and PSUs, Granted (shares) \| shares	1,972,614
Number of RSUs and PSUs, Released (shares) \| shares	(5,343,183)
Number of RSUs and PSUs, Canceled (shares) \| shares	(1,069,392)
Number of RSUs and PSUs Outstanding, Ending (shares) \| shares	6,364,847
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance (in dollars per share) \| $ / shares	$ 11.87
Weighted Average Grant Date Fair Value, Granted (in dollars per share) \| $ / shares	39.56
Weighted Average Grant Date Fair Value, Released (in dollars per share) \| $ / shares	9.94
Weighted Average Grant Date Fair Value, Canceled (in dollars per share) \| $ / shares	10.65
Weighted Average Grant Date Fair Value, Ending balance (in dollars per share) \| $ / shares	$ 22.28

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 623	$ 713	$ 1,832	$ 1,682

Restructuring Charges - Narrative (Details)	9 Months Ended
Restructuring Charges - Narrative (Details)	Sep. 30, 2019 position
2017 Restructuring Plan \| Workforce Reduction Costs
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated	55

Restructuring Charges - Restructuring Reserve (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Beginning balance			$ 448	$ 265	$ 265
Restructuring charges	$ 28	$ 17	97	252	589
Cash payments			(200)		(388)
Write-offs					(18)
Ending balance	43		43		448
2017 Restructuring Plan \| Workforce Reduction Costs
Restructuring Reserve [Roll Forward]
Beginning balance			146	44	44
Restructuring charges			97		253
Cash payments			(200)		(151)
Write-offs					0
Ending balance	43		43		146
2017 Restructuring Plan \| Lease Termination and Other Costs
Restructuring Reserve [Roll Forward]
Beginning balance			0	0	0
Restructuring charges			0		19
Cash payments			0		(19)
Write-offs					0
Ending balance	0		0		0
2015 Restructuring Plan \| Lease Termination and Other Costs
Restructuring Reserve [Roll Forward]
Beginning balance			302	$ 221	221
Restructuring charges			0		317
Cash payments			0		(218)
Write-offs					(18)
Ending balance	$ 0		0		$ 302
Accounting Standards Update 2016-02
Restructuring Reserve [Roll Forward]
Write-offs			(302)
Accounting Standards Update 2016-02 \| 2017 Restructuring Plan \| Workforce Reduction Costs
Restructuring Reserve [Roll Forward]
Write-offs			0
Accounting Standards Update 2016-02 \| 2017 Restructuring Plan \| Lease Termination and Other Costs
Restructuring Reserve [Roll Forward]
Write-offs			0
Accounting Standards Update 2016-02 \| 2015 Restructuring Plan \| Lease Termination and Other Costs
Restructuring Reserve [Roll Forward]
Write-offs			$ (302)

Related-Party Transactions (Details)	3 Months Ended		9 Months Ended
Related-Party Transactions (Details)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) board_member	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Adobe Systems \| Chief Executive Officer
Related Party Transaction [Line Items]
Purchases from related party	$ 400,000	$ 600,000	$ 1,900,000	$ 2,800,000
Revenue from related parties	0	0	0	100,000
Receivables from related party	0		0		$ 0
Cengage \| Chief Executive Officer
Related Party Transaction [Line Items]
Revenue from related parties	1,300,000	1,200,000	2,900,000	3,200,000
Due to related parties					$ 100,000
Cengage \| Board Of Directors Member
Related Party Transaction [Line Items]
Purchases from related party	4,200,000	3,800,000	$ 14,800,000	10,300,000
Number of board members appointed to Board of Directors of related party \| board_member			1
PayPal \| Board Of Directors Member
Related Party Transaction [Line Items]
Expenses from transactions with related party	400,000	$ 400,000	$ 1,200,000	$ 1,000,000.0
Synack, Inc. \| Board Of Directors Member
Related Party Transaction [Line Items]
Purchases from related party	$ 100,000		$ 400,000
Number of board members appointed to Board of Directors of related party \| board_member			1

Subsequent Event (Details) - Subsequent Event - USD ($)	Oct. 01, 2019	Oct. 07, 2019
Thinkful, Inc.
Subsequent Event [Line Items]
Cash paid to sellers at the closing of acquisition	$ 80,000,000.0
Potential additional payments, subject to performance-based contingencies	$ 20,000,000.0
Logistics And Warehousing Services \| FedEx
Subsequent Event [Line Items]
Fixed total commitments		$ 15,400,000

Label	Element	Value
Accounting Standards Update 2018-02 And 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (77,000)
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(111,000)
Accounting Standards Update 2018-02 And 2014-09 [Member] \| Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(77,000)
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (111,000)