Chegg (CHGG) 10-Q 29 Oct 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 26, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	CHEGG, INC
Entity Central Index Key	1,364,954
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		114,897,566

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 379,020	$ 126,457
Short-term investments	80,898	81,742
Accounts receivable, net of allowance for doubtful accounts of $268 and $259 at September 30, 2018 and December 31, 2017, respectively	8,620	10,855
Prepaid expenses	7,099	2,043
Other current assets	26,651	7,845
Total current assets	502,288	228,942
Long-term investments	14,961	20,305
Property and equipment, net	52,945	47,493
Goodwill	149,762	125,272
Intangible assets, net	27,813	21,153
Other assets	4,523	3,765
Total assets	752,292	446,930
Current liabilities
Accounts payable	4,283	7,049
Deferred revenue	25,281	13,440
Accrued liabilities	46,999	31,074
Total current liabilities	76,563	51,563
Long-term liabilities
Convertible senior notes, net	280,132	0
Other long-term liabilities	7,016	4,305
Total long-term liabilities	287,148	4,305
Total liabilities	363,711	55,868
Commitments and contingencies (Note 10)
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; 114,598,041 and 109,667,640 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	115	110
Additional paid-in capital	801,355	782,845
Accumulated other comprehensive loss	(965)	(282)
Accumulated deficit	(411,924)	(391,611)
Total stockholders' equity	388,581	391,062
Total liabilities and stockholders' equity	$ 752,292	$ 446,930

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable, current	$ 268	$ 259
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	114,598,041	109,667,640
Common stock, shares outstanding	114,598,041	109,667,640

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net revenues	$ 74,237	$ 62,640		$ 225,408	$ 181,559
Cost of revenues:	19,918	22,356		57,926	60,794
Gross profit	54,319	40,284		167,482	120,765
Operating expenses:
Research and development	29,045	19,876		80,796	59,077
Sales and marketing	15,690	14,184		42,463	40,246
General and administrative	20,000	17,320		57,735	47,163
Restructuring charges	17	64		252	1,023
Gain on liquidation of textbooks	0	0		0	(4,766)	[1]
Total operating expenses	64,752	51,444		181,246	142,743
Loss from operations	(10,433)	(11,160)		(13,764)	(21,978)
Interest expense and other income, net:
Interest expense, net	(3,772)	(19)		(7,456)	(56)
Other income, net	1,209	261		2,667	53
Total interest expense and other income, net	(2,563)	242		(4,789)	(3)
Loss before provision for income taxes	(12,996)	(10,918)		(18,553)	(21,981)
Provision for income taxes	713	598		1,682	1,961
Net loss	$ (13,709)	$ (11,516)	[1]	$ (20,235)	$ (23,942)	[1]
Net loss per share, basic and diluted (in dollars per share)	$ (0.12)	$ (0.11)		$ (0.18)	$ (0.25)
Weighted average shares used to compute net loss per share, basic and diluted (in shares)	114,184	103,041		112,621	97,008
[1]	Adjusted to reflect the adoption of ASU 2016-18. See Note 1 for more information.

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (13,709)	$ (11,516)	[1]	$ (20,235)	$ (23,942)	[1]
Other comprehensive (loss) income:
Change in net unrealized gain (loss) on available for sale investments	43	(48)		66	(48)
Change in foreign currency translation adjustments, net of tax	(347)	(9)		(749)	243
Other comprehensive (loss) income	(304)	(57)		(683)	195
Total comprehensive loss	$ (14,013)	$ (11,573)		$ (20,918)	$ (23,747)
[1]	Adjusted to reflect the adoption of ASU 2016-18. See Note 1 for more information.

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]
Cash flows from operating activities
Net loss	$ (20,235)	$ (23,942)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization expense	16,631	14,301
Share-based compensation expense	37,503	27,468
Gain on liquidation of textbooks	0	(4,766)
Loss from write-offs of textbooks	0	314
Loss from write-off of property and equipment	29	1,368
Interest accretion on deferred consideration	0	(626)
Amortization of debt discount and issuance costs	6,958	0
Deferred income taxes	(315)	0
Other non-cash items	51	62
Change in assets and liabilities:
Accounts receivable	2,409	786
Prepaid expenses and other current assets	(24,250)	(4,293)
Other assets	(587)	333
Accounts payable	(3,001)	(2,291)
Deferred revenue	11,841	7,070
Accrued liabilities	16,044	12,880
Other liabilities	1,589	1,123
Net cash provided by operating activities	44,667	29,787
Cash flows from investing activities
Proceeds from liquidations of textbooks	0	6,943
Purchases of marketable securities	(113,276)	(112,417)
Proceeds from sale of marketable securities	1,800	14,499
Maturities of marketable securities	118,080	0
Purchases of property and equipment	(18,048)	(19,930)
Acquisition of businesses, net of cash acquired	(34,650)	0
Net cash used in investing activities	(46,094)	(110,905)
Cash flows from financing activities
Common stock issued under stock plans, net	23,463	13,565
Payment of taxes related to the net share settlement of equity awards	(45,669)	(17,902)
Payment of deferred cash consideration related to acquisitions	0	(16,939)
Proceeds from follow-on offering, net of offering costs	0	147,632
Proceeds from issuance of convertible senior notes, net of issuance costs	335,618	0
Purchase of convertible senior notes capped call	(39,227)	0
Repurchase of common stock	(20,000)	0
Net cash provided by financing activities	254,185	126,356
Net increase in cash, cash equivalents and restricted cash	252,758	45,238
Cash, cash equivalents and restricted cash, beginning of period	126,963	77,433
Cash, cash equivalents and restricted cash, end of period	379,721	122,671
Supplemental cash flow data:
Interest	55	66
Income taxes	1,560	1,241
Non-cash investing and financing activities:
Accrued purchases of long-lived assets	$ 2,993	$ 3,712
[1]	Adjusted to reflect the adoption of ASU 2016-18. See Note 1 for more information.

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - Reconciliation of cash, cash equivalents and restricted cash - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	[1]
Statement of Cash Flows [Abstract]
Cash and cash equivalents	$ 379,020	$ 122,227
Restricted cash included in other assets	701	444
Total cash, cash equivalents and restricted cash	$ 379,721	$ 122,671
[1]	Adjusted to reflect the adoption of ASU 2016-18. See Note 1 for more information.

Background and Basis of Present

Background and Basis of Presentation	9 Months Ended
	Sep. 30, 2018
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 the 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, 2018 , the condensed consolidated statements of operations and the condensed consolidated statements of comprehensive loss for the three and nine months ended September 30, 2018 and 2017 , the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017 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, 2018 , our results of operations for the three and nine months ended September 30, 2018 and 2017 , and cash flows for the nine months ended September 30, 2018 and 2017 . Our results of operations and cash flows for the nine months ended September 30, 2018 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, 2017 as 2017 . 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, 2017 (the Annual Report on Form 10-K) filed with the U.S. Securities and Exchange Commission (SEC). We have changed the caption on our condensed consolidated statements of operations from “technology and development” to “research and development.” This change does not impact any current or previously reported amounts. Except for our policies on revenue recognition, deferred revenue 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. Revenue Recognition and Deferred Revenue We recognize revenues from our Chegg Services and Required Materials offerings when control of the 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. We determine revenue recognition through the following steps: • Identification of the contract, or contracts, with a customer • Identification of the performance obligations in the contract • Determination of the transaction price • Allocation of the transaction price to the performance obligations in the contract • Recognition of revenue when, or as, we satisfy a performance obligation We generate revenues from our Chegg Services product line including our Chegg Study service, our Chegg Writing service, our Chegg Tutors service, Test Prep, through our partnership with Kaplan Test Prep (Kaplan), Internship services, Brand Partnership services that we offer to brands and Enrollment Marketing services to colleges, through our strategic partnership with the National Research Center for College and University Admissions (NRCCUA). Chegg Services are offered to students through weekly, monthly or annual subscriptions, and we primarily recognize revenues ratably over the respective subscription period. Enrollment Marketing services and Brand Partnership services are offered either on a subscription or on an a la carte basis. Revenues are recognized ratably or as earned over the subscription service period, generally one year. Revenues from Enrollment Marketing services or Brand Partnership services delivered on an a la carte basis, without a subscription, are recognized when delivery of the respective lead or service has occurred. Historically, under previous revenue recognition guidance, revenue recognition was delayed for certain contracts with extended payment terms. For these services, we bill the customer at the inception, over the term of the customer arrangement or as the services are performed. Upon satisfactory assessment of creditworthiness, we generally grant credit to our Enrollment Marketing and Brand Partnership customers with normal credit terms, typically 30 days. Some of our customer arrangements for Brand Partnership and Enrollment Marketing services include multiple performance obligations. We have determined these performance obligations qualify as distinct performance obligations, as the customer can benefit from the service on its own or together with other resources that are readily available to the customer and our promise to transfer the service is separately identifiable from other promises in the contract. For these arrangements that contain distinct performance obligations, we allocate the transaction price based on the relative standalone selling price method by comparing the standalone selling price (SSP) of each distinct performance obligation to the total value of the contract. We determine the SSP based on our historical pricing and discounting practices for the distinct performance obligation when sold separately. If the SSP is not directly observable, we estimate the SSP by considering information such as market conditions, and information about the customer. Additionally, we limit the amount of revenues recognized for delivered promises to the amount that is not contingent on future delivery of services or other future performance obligations. We also generate revenues from our Required Materials product line including revenue share earned on print textbooks for rental or sale transactions, owned by Ingram and other partners, which are recognized immediately when a book ships to the student. Revenues from the rental or sale of eTextbooks is recognized ratably over the contractual period, generally two to five months, or at time of the sale, respectively. Our strategic partnership with Ingram includes an amount of variable consideration in addition to a fixed revenue share that we earn. This variable consideration can either increase or decrease the total transaction price depending on the nature of the variable consideration. Under the new revenue recognition guidance, we estimate the amount of variable consideration that we will earn at the inception of the contract, adjusted during each period, and include an estimated amount each period as opposed to the contractual amount earned under the previous revenue recognition guidance. For sales of third party products, we evaluate whether we are acting as a principal or an agent, and therefore would record the gross sales amount as revenues and related costs or the net amount earned as a revenue share from the sale of third party products. Our determination is based on our evaluation of whether we control the specified goods or services prior to transferring them to the customer. For our strategic partnership with Ingram and our agreements with other textbook publishers, we have concluded that we do not control the use of the print textbooks, and therefore record net revenue only for the revenue share we earn upon the shipment of a print textbook to a student. For the rental or sale of eTextbooks, we have concluded that we control the service, therefore we recognize revenue and cost of revenue on a gross basis ratably over the term the student has access to the eTextbook. Revenues are presented net of sales tax collected from customers to be remitted to governmental authorities and net of allowances for estimated cancellations and customer returns, which are based on historical data. Customer refunds from cancellations and returns are recorded as a reduction to revenues. Contract assets are contained within other current assets on our condensed consolidated balance sheets. Contract assets represent the goods or services that we have transferred to a customer before invoicing the customer. Contract receivables are contained within accounts receivable, net on our condensed consolidated balance sheets and represent unconditional consideration that will be received solely due to the passage of time. Contract liabilities are contained within deferred revenue on our condensed consolidated balance sheets. Deferred revenue primarily consists of advanced payments from students related to rental and subscription performance obligations that have not been satisfied, Brand Partnership and Enrollment Marketing performance obligations that have yet to be satisfied, and the estimated variable consideration as a result of our strategic partnership with Ingram. Deferred revenue related to rental and subscription performance obligations is recognized as revenues ratably over the term for subscriptions or when the services are provided and all other revenue recognition criteria have been met. Deferred revenue related to variable consideration is recognized as revenues during each reporting period based on the estimated amount we believe we will earn over the life of the contract. Convertible Senior Notes, net In April 2018 , we issued $345 million in aggregate principal amount of 0.25% convertible senior notes due in 2023 (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 sheet, 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 including variable consideration, recoverability of accounts receivable, fair value of debt and equity components related to our convertible senior notes, restructuring charges, share-based compensation expense including estimated forfeitures, accounting for income taxes, useful lives assigned to long-lived assets for depreciation and amortization, valuation of goodwill and long-lived assets, and the valuation of acquired intangible assets. 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 August 2018, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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, and we are currently in the process of evaluating the impact of this guidance. The FASB has issued three ASU's related to Accounting Standards Codification (ASC) 842. 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). ASU 2016-02 requires an entity to recognize a right-of-use 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. ASC 842 allows for 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 plan to elect this package of transition practical expedients. ASU 2018-10 provides additional updates and corrections to topics included within ASC 842 based on the FASB's interactions with stakeholders. ASU 2018-11 allows for a modified retrospective adoption with a cumulative-effect adjustment to the opening balance of accumulated deficit in the period of adoption. We plan to elect this transition method of adoption. Early adoption is permitted and the guidance is effective for annual periods beginning after December 15, 2018. We plan to adopt the guidance on January 1, 2019. At this time, we do not know the quantitative impact of adopting ASU 2016-02; however, we initially believe that this will only have an impact on our condensed consolidated balance sheet and little to no impact to our condensed consolidated statement of operations. We will continue to evaluate as we near our adoption date. 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 In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting . ASU 2018-07 expands the scope of Topic 718, Compensation—Stock Compensation to include share-based payment transactions for acquiring goods and services from non-employees. These awards are measured at the grant-date fair value of the equity instruments that an entity is obligated to issue when the good has been delivered or the service has been rendered and any other conditions necessary to earn the right to benefit from the instruments have been satisfied. The guidance is effective for annual periods after December 15, 2018, with early adoption permitted, and the guidance requires a modified retrospective application to awards that have not been settled as of the adoption date. We have elected to early adopt this guidance during the second quarter of 2018 and our adoption did not result in an adjustment to the opening balance of accumulated deficit. In February 2018, the FASB issued ASU No. 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . ASU 2018-02 allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. We adopted the guidance on January 1, 2018 recording an immaterial reclassification from accumulated other comprehensive income (loss) to the opening balance of accumulated deficit. In January 2017, the FASB issued ASU No. 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment . ASU 2017-04 eliminates step 2 from the annual goodwill impairment test no longer requiring the comparison of the implied fair value of a reporting unit's goodwill with the carrying amount of goodwill. We early adopted the guidance to simplify our goodwill impairment test, with a prospective application on January 1, 2018 and will apply the guidance starting with our 2018 annual goodwill impairment assessment. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business . ASU 2017-01 clarifies the definition of a business to assist entities with evaluating whether a transaction should be accounted for as acquisitions of assets or businesses. We adopted the guidance with a prospective application on January 1, 2018. We will analyze the clarified definition of a business to determine whether transactions from our application date should be accounted for as an asset acquisition or business combination under the new guidance. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . ASU 2016-18 requires an entity to explain the change during a period in restricted cash equivalents on the condensed consolidated statements of cash flows and include such amounts when reconciling beginning-of-period and end-of-period total amounts shown on the condensed consolidated statements of cash flows. We adopted the guidance with a retrospective application on January 1, 2018 and have adjusted our beginning-of-period and end-of-period amounts on our condensed consolidated statement of cash flows to include restricted cash with the change in restricted cash included within the other assets line on our condensed consolidated statement of cash flows. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . ASU 2016-01 requires entities to measure equity investments at fair value and recognize any changes in fair value within the condensed consolidated statement of operations. We have a strategic investment of $3.0 million recorded in other assets on our condensed consolidated balance sheets that falls under this guidance update. The guidance provides for electing a measurement alternative for equity investments that do not have readily determinable fair values. We have elected the measurement alternative for our strategic investment as there is not a readily determinable fair value, which we will apply to our strategic investment starting with our adoption date of January 1, 2018. This investment will be measured at cost, less any impairment, plus or minus adjustments resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer , with any changes in the value of the investment recorded within the condensed consolidated statement of operations. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, as amended (Topic 606) (ASC 606), which changes the way we recognize revenue and significantly expands the disclosure requirements for revenue arrangements. We adopted ASU 2014-09 under the modified retrospective application, recording the cumulative effect of adoption as an adjustment to the opening balance of accumulated deficit on our adoption date of January 1, 2018. We have not adjusted previously reported amounts. Adoption of the new standard resulted in changes to our accounting policies for revenue recognition, and trade and other receivables. See Note 2 for more information.

Revenues

Revenues	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenues	Revenues Adoption of ASC Topic 606, Revenue from Contracts with Customers On January 1, 2018, we adopted the new revenue recognition guidance using the modified retrospective method applied to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning January 1, 2018 are presented under the new revenue recognition guidance, while prior period amounts were not adjusted and continue to be reported in accordance with the previous revenue recognition guidance. We recorded an immaterial net increase to the opening balance of accumulated deficit as of January 1, 2018 due to the cumulative impact of adopting the new revenue recognition guidance. The two primary impacts of the new revenue recognition guidance are for our Enrollment Marketing services where revenue is recognized earlier in the contract life under the new revenue recognition guidance than under the previous guidance and for our strategic partnership with Ingram where we are required to estimate variable consideration under the new revenue recognition guidance, which we were not previously required to estimate. The requirement to estimate variable consideration has shifted $1.0 million and $2.1 million of revenues during the three and nine months ended September 30, 2018 , respectively, to future periods as compared to the previous revenue recognition guidance. 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 Ingram and other partners, being recognized at the point in time when print textbooks are shipped to students. The following table sets 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 Change 2018 2017 (1) $ % Chegg Services $ 54,201 $ 39,475 $ 14,726 37 % Required Materials 20,036 23,165 (3,129 ) (14 )% Total net revenues $ 74,237 $ 62,640 $ 11,597 19 % Nine Months Ended Change 2018 2017 (1) $ % Chegg Services $ 172,327 $ 125,210 $ 47,117 38 % Required Materials 53,081 56,349 (3,268 ) (6 )% Total net revenues $ 225,408 $ 181,559 $ 43,849 24 % (1) As noted above, prior period amounts have not been adjusted under the modified retrospective method. During the three months ended September 30, 2018 , we recognized $10.8 million of revenues that were included in our deferred revenue balance as of June 30, 2018. During the nine months ended September 30, 2018 , we recognized $11.7 million of revenues that were included in our deferred revenue balance as of December 31, 2017 . During the three and nine months ended September 30, 2018 , there was an immaterial amount of revenues recognized from performance obligations satisfied in previous periods. The aggregate amount of unsatisfied performance obligations is approximately $29.0 million as of September 30, 2018 , of which a majority is expected to be recognized into revenues over the next year and the remainder within three years. As a practical expedient, we do not disclose the value of unsatisfied performance obligations for contracts with an expected duration of one year or less. Contract Balances The following table presents our accounts receivable, net and deferred revenue balances (in thousands, except percentages): Change September 30, 2018 December 31, 2017 $ % Accounts receivable, net $ 8,620 $ 10,855 $ (2,235 ) (21 )% Deferred revenue $ 25,281 $ 13,440 $ 11,841 88 % During the nine months ended September 30, 2018 , our accounts receivable, net balance decreased by $2.2 million , or 21% , primarily due to an improvement in cash collections. During the nine months ended September 30, 2018 , our deferred revenue balance increased by $11.8 million , or 88% , primarily due to increased bookings for our Chegg Study service and eTextbook rentals as well as the deferred variable consideration as a result of our strategic partnership with Ingram. Our contract assets balance was immaterial as of September 30, 2018 and December 31, 2017 .

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing 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, warrants, shares related to convertible senior notes, restricted stock units (RSUs), and performance-based restricted stock units (PSUs), 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 historical basic and diluted net loss per share (in thousands, except per share amounts): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Numerator: Net loss $ (13,709 ) $ (11,516 ) $ (20,235 ) $ (23,942 ) Denominator: Weighted average shares used to compute net loss per share, basic and diluted 114,184 103,041 112,621 97,008 Net loss per share, basic and diluted $ (0.12 ) $ (0.11 ) $ (0.18 ) $ (0.25 ) 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 Nine Months Ended 2018 2017 2018 2017 Options to purchase common stock 3,961 2 4,282 3,167 RSUs and PSUs 7,479 49 8,075 137 Shares related to convertible senior notes 1,221 — — — Employee stock purchase plan 17 — 12 — Warrants to purchase common stock — — — 200 Total common stock equivalents 12,678 51 12,369 3,504

Cash and Cash Equivalents, and

Cash and Cash Equivalents, and Investment	9 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Cash and Cash Equivalents, and Investment	Cash and Cash Equivalents, and Investments The following table shows our cash and cash equivalents, and investments’ cost, net unrealized loss and fair value as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Cost Net Unrealized Loss Fair Value Cost Net Unrealized Loss Fair Value Cash and cash equivalents: Cash $ 340,933 $ — $ 340,933 $ 98,370 $ — $ 98,370 Money market funds 7,017 — 7,017 5,358 — 5,358 Commercial paper 31,071 (1 ) 31,070 22,729 — 22,729 Total cash and cash equivalents $ 379,021 $ (1 ) $ 379,020 $ 126,457 $ — $ 126,457 Short-term investments: Commercial paper $ 29,461 $ (1 ) $ 29,460 $ 38,850 $ (27 ) $ 38,823 Corporate securities 40,658 (103 ) 40,555 23,001 (43 ) 22,958 U.S. treasury securities 10,891 (8 ) 10,883 19,978 (17 ) 19,961 Total short-term investments $ 81,010 $ (112 ) $ 80,898 $ 81,829 $ (87 ) $ 81,742 Long-term investments: Corporate securities $ 13,343 $ (1 ) $ 13,342 $ 20,405 $ (100 ) $ 20,305 U.S. treasury securities 1,626 (7 ) 1,619 — — — Total long-term investments $ 14,969 $ (8 ) $ 14,961 $ 20,405 $ (100 ) $ 20,305 The cost and fair value of available-for-sale investments as of September 30, 2018 by contractual maturity were as follows (in thousands): Cost Fair Value Due in 1 year or less $ 112,081 $ 111,968 Due in 1-2 years 14,969 14,961 Investments not due at a single maturity date 7,017 7,017 Total $ 134,067 $ 133,946 Investments not due at a single maturity date in the preceding table consist of money market fund deposits. As of September 30, 2018 , 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 do not intend to sell the investments nor is it more likely than not that we will be required to sell the investments before recovery of their cost bases. We typically invest in highly-rated securities with a minimum credit rating of A- and a weighted average maturity of five months, and our investment policy generally limits the amount of credit exposure to any one issuer. 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, 2018 and 2017 , we did not recognize any impairment charges. Restricted Cash As of September 30, 2018 and December 31, 2017 , we had approximately $0.7 million and $0.5 million , respectively, of restricted cash that consists of security deposits for our offices. These amounts are classified in either other current assets or other assets on our condensed consolidated balance sheets based on the remaining term of the lease from the balance sheet dates. Strategic Investment We previously invested $3.0 million in a foreign entity to explore expanding our reach internationally. Our investment is included in other assets on our condensed consolidated balance sheets. We did not record an impairment charge on this investment during the three and nine months ended September 30, 2018 and 2017 , as there were no significant identified events or changes in circumstances that would be considered an indicator for impairment. Further, there were no observable price changes in orderly transactions for the identical or a similar investment of the same issuer during the three and nine months ended September 30, 2018 .

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurement	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, 2018 and December 31, 2017 are classified based on the valuation technique level in the tables below (in thousands): September 30, 2018 Total Quoted Prices Significant Assets: Cash equivalents: Money market funds $ 7,017 $ 7,017 $ — Commercial paper 31,070 — 31,070 Short-term investments: Commercial paper 29,460 — 29,460 Corporate securities 40,555 — 40,555 U.S. treasury securities 10,883 10,883 — Long-term investments: Corporate securities 13,342 — 13,342 U.S. treasury securities 1,619 1,619 — Total assets measured and recorded at fair value $ 133,946 $ 19,519 $ 114,427 December 31, 2017 Total Quoted Prices Significant Assets: Cash equivalents: Money market funds $ 5,358 $ 5,358 $ — Commercial paper 22,729 — 22,729 Short-term investments: — Commercial paper 38,823 — 38,823 Corporate securities 22,958 — 22,958 U.S. treasury securities 19,961 19,961 — Long-term corporate securities 20,305 — 20,305 Total assets measured and recorded at fair value $ 130,134 $ 25,319 $ 104,815 We value our marketable securities 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 marketable securities 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 notes are measured at fair value, utilizing a level 2 input, on a quarterly basis for disclosure purposes. The carrying amounts and estimated fair values of financial instruments not recorded at fair value as of September 30, 2018 are as follows (in thousands): September 30, 2018 Carrying Amount Estimated Fair Value Convertible senior notes, net $ 280,132 $ 411,143 The carrying amount of the notes as of September 30, 2018 was net of unamortized debt discount of $58.0 million and unamortized issuance costs of $6.9 million . The estimated fair value of the notes was determined based on the closing 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 8.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions	Acquisitions On July 2, 2018, we acquired StudyBlue, Inc. (StudyBlue), a privately held online learning company based in San Francisco, California that provides a content library that allows students to create flashcards and their own study materials. This acquisition helps strengthen our existing Chegg Services offerings by adding a substantial number of subject categories and a library of content to our learning platform. The total fair value of the purchase consideration was $20.4 million , which included an escrow amount of $3.3 million for general representations and warranties and post-closing adjustments. Any remaining escrow amount will be released eighteen months after the acquisition date. On May 15, 2018, we acquired WriteLab, Inc. (WriteLab), an AI-enhanced writing platform, based in Berkeley, California, that teaches students grammar, sentence structure, writing style, and offers instant feedback to help students revise, edit, and improve their written work. This acquisition helps to strengthen our existing Chegg Writing service with the addition of new tools, features, and functionality. The total fair value of the purchase consideration was $14.5 million , which included an escrow amount of $2.6 million for general representations and warranties and potential post-closing adjustments. Any remaining escrow amount will be released twenty months after the acquisition date. The acquisition date fair value of the purchase consideration for the above transactions consisted of the following (in thousands): Initial cash consideration $ 29,980 Escrow 5,820 Net working capital adjustment (916 ) Fair value of purchase consideration $ 34,884 Included in the purchase agreement for the acquisition of WriteLab are additional contingent payments of up to $5.0 million subject to continued employment of the sellers. These payments are expensed ratably as research and development expenses on our condensed consolidated statement of operations. These contingent payments may be settled by us, at our sole discretion, either in cash or shares of our common stock. We have recorded approximately $0.6 million as of September 30, 2018 included within accrued liabilities on our condensed consolidated balance sheet for these contingent payments. The fair value of the intangible assets acquired was determined under the acquisition method of accounting for business combinations. The excess of the purchase consideration paid over the fair value of net identifiable assets acquired was recorded as goodwill. Goodwill is primarily attributable to the potential for future product offerings as well as our expanded student reach. The amounts recorded for intangible assets and goodwill are not deductible for tax purposes. The following table presents the total allocation of purchase consideration recorded in our condensed consolidated balance sheets as of the acquisition date (in thousands): Cash $ 234 Accounts receivable 302 Other acquired assets 151 Acquired intangible assets: Trade name 140 Domain names 180 Non-compete agreements 220 Developed technology 5,790 Content library 5,220 Total acquired intangible assets 11,550 Total identifiable assets acquired 12,237 Liabilities assumed (2,133 ) Net identifiable assets acquired 10,104 Goodwill 24,780 Total fair value of purchase consideration $ 34,884 During the three and nine months ended September 30, 2018 , we incurred $0.6 million and $1.0 million , respectively, of acquisition-related expenses which have been included in general and administrative expenses in our condensed consolidated statement of operations. We have not presented supplemental pro forma financial information as the revenues and earnings of these acquisitions were immaterial during the nine months ended September 30, 2018 . Further, we have recorded no revenues and an immaterial amount of expenses since the acquisition dates.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill consists of the following (in thousands): Nine Months Ended Year Ended December 31, 2017 Beginning balance $ 125,272 $ 116,239 Additions due to acquisitions 24,780 9,024 Foreign currency translation adjustment (290 ) 9 Ending balance $ 149,762 $ 125,272 Intangible assets as of September 30, 2018 and December 31, 2017 consist of the following (in thousands, except the weighted-average amortization period in months): September 30, 2018 Weighted-Average Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Developed technologies 71 $ 31,667 $ (12,655 ) $ 19,012 Customer lists 47 9,970 (6,505 ) 3,465 Trade names 44 6,113 (4,542 ) 1,571 Non-compete agreements 31 2,018 (1,668 ) 350 Master service agreements 21 1,030 (1,030 ) — Indefinite-lived trade name — 3,600 — 3,600 Foreign currency translation adjustment — (185 ) — (185 ) Total intangible assets 61 $ 54,213 $ (26,400 ) $ 27,813 December 31, 2017 Weighted-Average Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Developed technologies 70 $ 20,657 $ (10,220 ) $ 10,437 Customer lists 47 9,970 (5,480 ) 4,490 Trade names 46 5,793 (3,465 ) 2,328 Non-compete agreements 30 1,798 (1,506 ) 292 Master service agreements 21 1,030 (1,030 ) — Indefinite-lived trade name — 3,600 — 3,600 Foreign currency translation adjustment — 6 — 6 Total intangible assets 57 $ 42,854 $ (21,701 ) $ 21,153 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. During the three and nine months ended September 30, 2017 , amortization expense related to our acquired intangible assets totaled approximately $1.4 million and $4.1 million , respectively. As of September 30, 2018 , the estimated future amortization expense related to our finite-lived intangible assets is as follows (in thousands): Remaining three months of 2018 $ 1,811 2019 6,448 2020 4,816 2021 3,423 2022 2,943 Thereafter 4,772 Total $ 24,213

Convertible Senior Notes

Convertible Senior Notes	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Convertible Senior Notes	Convertible Senior Notes In April 2018 , we issued $345 million in aggregate principal amount of 0.25% convertible senior notes due in 2023 (the notes), in a private placement to qualified institutional buyers pursuant to Rule 144A of the Securities Act of 1933, as amended. The aggregate principal amount of the notes includes $45 million from initial purchasers fully exercising their option to purchase additional notes. The total net proceeds from the notes are as follows (in thousands): Principal amount $ 345,000 Less initial purchasers’ discount (8,625 ) Less other issuance costs (757 ) Net proceeds $ 335,618 The notes are our senior, unsecured obligations and 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 notes will mature on May 15, 2023 (the maturity date), unless repurchased, redeemed or converted in accordance with their terms prior to such date. The terms of the notes are governed by an indenture agreement by and between us and Wells Fargo Bank, National Association, as Trustee (the indenture). Each $1,000 principal amount of the 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 February 15, 2023 , 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, 2018, 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 conversion price for the notes on each applicable trading day; • during the five business day period after any ten 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 indenture. On or after February 15, 2023 until the close of business on the second scheduled trading day immediately preceding the maturity date, 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 indenture, prior to the maturity date, 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 indenture, occur prior to the applicable maturity date, 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 months ended September 30, 2018 , the conditions allowing holders of the notes to convert have not been met. The notes are therefore not convertible during the three months ended September 30, 2018 and are classified as long-term debt. In accounting for the issuance of the notes, we separated the notes into liability and equity components. The carrying amount of the liability component of approximately $280.8 million 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 component of approximately $64.2 million , representing the conversion option, was determined by deducting the carrying amount of the liability component from the principal amount of the notes. This difference between the principal amount of the notes and the liability component represents the debt discount, presented as a reduction to the convertible debt on our condensed consolidated balance sheet, and is amortized to interest expense using the effective interest method over the remaining term of the notes. The equity component of the notes is included in additional paid-in capital on our condensed consolidated balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. We incurred issuance costs related to the 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 principal amount of the notes. Transaction costs attributable to the liability component of approximately $7.6 million , were recorded as debt issuance cost, presented as a reduction to the convertible debt on our condensed consolidated balance sheet, and are amortized to interest expense using the effective interest method over the term of the notes. The issuance costs attributable to the equity component were approximately $1.7 million 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): As of September 30, 2018 Principal $ 345,000 Unamortized debt discount (57,976 ) Unamortized issuance costs (6,892 ) Net carrying amount $ 280,132 The net carrying amount of the equity component of the notes is as follows (in thousands): As of September 30, 2018 Debt discount for conversion option $ 64,193 Issuance costs (1,749 ) Net carrying amount $ 62,444 As of September 30, 2018 , the remaining life of the notes is approximately 4.6 years. Based on the closing price of our common stock of $28.43 on September 30, 2018 , the if-converted value of the notes was approximately $363.9 million and exceeds the principal amount of $345 million by approximately $18.9 million . The effective interest rate of the liability component of the notes is 4.34% and is based on the interest rate of similar debt instruments, at the time of our offering, that do not have an associated convertible feature. The following table sets forth the total interest expense recognized related to the notes (in thousands): Three Months Ended Nine Months Ended Contractual interest expense $ 218 $ 428 Amortization of debt discount 3,160 6,217 Amortization of issuance costs 377 741 Total interest expense $ 3,755 $ 7,386 Capped Call Transactions Concurrently with the offering of the notes in April 2018, we used $39.2 million 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 cover approximately 12,801,260 shares of our common stock and are intended to effectively increase the overall conversion price from $26.95 to $40.68 per share. 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 sheet 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 Chegg’s common stock exceeds the conversion price of $26.95 per share 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 the conversion price. However, as a result of the capped call transactions described above, there will be no economic dilution from the notes up to $40.68 , as exercise of the capped call instruments will reduce any dilution from the notes that would have otherwise occurred when the price of our common stock exceeds the conversion price. Revolving Line of Credit In September 2016, we entered into a revolving line of credit, which was amended in March 2018, with an aggregate principal amount of $30.0 million (the Line of Credit) with an accordion feature that, subject to the lender's discretion, allows us to borrow up to a total of $50.0 million . The Line of Credit expires in September 2019 and requires us to repay the outstanding balance upon maturity. We will pay a fee equal to 0.25% per year on the average daily unused amount of the Line of Credit and a base interest rate equal to the LIBOR. In addition, we will pay a fee for each issued letter of credit which will be determined based on our current leverage ratio at the time the letter of credit is issued. If our leverage ratio is less than 1.00% , we will pay a fee equal to 1.50% per year and if our leverage ratio is greater than or equal to 1.00% , we will pay a fee equal to 2.50% per year. Our leverage ratio is a ratio of all obligations owed to the bank divided by our consolidated EBITDA. EBITDA for the purposes of calculating our leverage ratio is defined as net profit (loss) before tax, plus interest expense and amortized debt issuance costs, plus non-cash stock compensation (net of capitalized interest expense), plus depreciation expense, plus amortization expense and other non-cash expenses (assuming there are no future cash costs), plus expenses incurred in connection with permitted acquisitions (including without limitation accrued acquisition-related contingent expenses) in an amount not to exceed $6.0 million per calendar year, plus non-recurring expenses in an amount not to exceed $2.0 million per calendar year. We must maintain financial covenants under the Line of Credit as follows: (1) maintain a balance of unrestricted cash at the lender of not less than $30.0 million at all times, other than the three months ending March 31, 2017 and June 30, 2017, and not less than $25.0 million during the three months ending March 31, 2017 and June 30, 2017; and (2) achieve EBITDA, on a trailing 12 month basis, of not less than (i) $25.0 million for the period of time from September 30, 2016 through June 30, 2017, (ii) $30.0 million for the period of time from September 30, 2017 through June 30, 2018, and (iii) $35.0 million for the period of time from September 30, 2018 through the maturity of the Line of Credit. As of September 30, 2018 , we were in compliance with the financial covenants of the Line of Credit. Further, we had no amounts outstanding and were able to borrow up to $30.0 million under the Line of Credit.

Revolving Line of Credit

Revolving Line of Credit	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Revolving Line of Credit	Convertible Senior Notes In April 2018 , we issued $345 million in aggregate principal amount of 0.25% convertible senior notes due in 2023 (the notes), in a private placement to qualified institutional buyers pursuant to Rule 144A of the Securities Act of 1933, as amended. The aggregate principal amount of the notes includes $45 million from initial purchasers fully exercising their option to purchase additional notes. The total net proceeds from the notes are as follows (in thousands): Principal amount $ 345,000 Less initial purchasers’ discount (8,625 ) Less other issuance costs (757 ) Net proceeds $ 335,618 The notes are our senior, unsecured obligations and 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 notes will mature on May 15, 2023 (the maturity date), unless repurchased, redeemed or converted in accordance with their terms prior to such date. The terms of the notes are governed by an indenture agreement by and between us and Wells Fargo Bank, National Association, as Trustee (the indenture). Each $1,000 principal amount of the 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 February 15, 2023 , 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, 2018, 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 conversion price for the notes on each applicable trading day; • during the five business day period after any ten 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 indenture. On or after February 15, 2023 until the close of business on the second scheduled trading day immediately preceding the maturity date, 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 indenture, prior to the maturity date, 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 indenture, occur prior to the applicable maturity date, 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 months ended September 30, 2018 , the conditions allowing holders of the notes to convert have not been met. The notes are therefore not convertible during the three months ended September 30, 2018 and are classified as long-term debt. In accounting for the issuance of the notes, we separated the notes into liability and equity components. The carrying amount of the liability component of approximately $280.8 million 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 component of approximately $64.2 million , representing the conversion option, was determined by deducting the carrying amount of the liability component from the principal amount of the notes. This difference between the principal amount of the notes and the liability component represents the debt discount, presented as a reduction to the convertible debt on our condensed consolidated balance sheet, and is amortized to interest expense using the effective interest method over the remaining term of the notes. The equity component of the notes is included in additional paid-in capital on our condensed consolidated balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. We incurred issuance costs related to the 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 principal amount of the notes. Transaction costs attributable to the liability component of approximately $7.6 million , were recorded as debt issuance cost, presented as a reduction to the convertible debt on our condensed consolidated balance sheet, and are amortized to interest expense using the effective interest method over the term of the notes. The issuance costs attributable to the equity component were approximately $1.7 million 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): As of September 30, 2018 Principal $ 345,000 Unamortized debt discount (57,976 ) Unamortized issuance costs (6,892 ) Net carrying amount $ 280,132 The net carrying amount of the equity component of the notes is as follows (in thousands): As of September 30, 2018 Debt discount for conversion option $ 64,193 Issuance costs (1,749 ) Net carrying amount $ 62,444 As of September 30, 2018 , the remaining life of the notes is approximately 4.6 years. Based on the closing price of our common stock of $28.43 on September 30, 2018 , the if-converted value of the notes was approximately $363.9 million and exceeds the principal amount of $345 million by approximately $18.9 million . The effective interest rate of the liability component of the notes is 4.34% and is based on the interest rate of similar debt instruments, at the time of our offering, that do not have an associated convertible feature. The following table sets forth the total interest expense recognized related to the notes (in thousands): Three Months Ended Nine Months Ended Contractual interest expense $ 218 $ 428 Amortization of debt discount 3,160 6,217 Amortization of issuance costs 377 741 Total interest expense $ 3,755 $ 7,386 Capped Call Transactions Concurrently with the offering of the notes in April 2018, we used $39.2 million 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 cover approximately 12,801,260 shares of our common stock and are intended to effectively increase the overall conversion price from $26.95 to $40.68 per share. 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 sheet 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 Chegg’s common stock exceeds the conversion price of $26.95 per share 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 the conversion price. However, as a result of the capped call transactions described above, there will be no economic dilution from the notes up to $40.68 , as exercise of the capped call instruments will reduce any dilution from the notes that would have otherwise occurred when the price of our common stock exceeds the conversion price. Revolving Line of Credit In September 2016, we entered into a revolving line of credit, which was amended in March 2018, with an aggregate principal amount of $30.0 million (the Line of Credit) with an accordion feature that, subject to the lender's discretion, allows us to borrow up to a total of $50.0 million . The Line of Credit expires in September 2019 and requires us to repay the outstanding balance upon maturity. We will pay a fee equal to 0.25% per year on the average daily unused amount of the Line of Credit and a base interest rate equal to the LIBOR. In addition, we will pay a fee for each issued letter of credit which will be determined based on our current leverage ratio at the time the letter of credit is issued. If our leverage ratio is less than 1.00% , we will pay a fee equal to 1.50% per year and if our leverage ratio is greater than or equal to 1.00% , we will pay a fee equal to 2.50% per year. Our leverage ratio is a ratio of all obligations owed to the bank divided by our consolidated EBITDA. EBITDA for the purposes of calculating our leverage ratio is defined as net profit (loss) before tax, plus interest expense and amortized debt issuance costs, plus non-cash stock compensation (net of capitalized interest expense), plus depreciation expense, plus amortization expense and other non-cash expenses (assuming there are no future cash costs), plus expenses incurred in connection with permitted acquisitions (including without limitation accrued acquisition-related contingent expenses) in an amount not to exceed $6.0 million per calendar year, plus non-recurring expenses in an amount not to exceed $2.0 million per calendar year. We must maintain financial covenants under the Line of Credit as follows: (1) maintain a balance of unrestricted cash at the lender of not less than $30.0 million at all times, other than the three months ending March 31, 2017 and June 30, 2017, and not less than $25.0 million during the three months ending March 31, 2017 and June 30, 2017; and (2) achieve EBITDA, on a trailing 12 month basis, of not less than (i) $25.0 million for the period of time from September 30, 2016 through June 30, 2017, (ii) $30.0 million for the period of time from September 30, 2017 through June 30, 2018, and (iii) $35.0 million for the period of time from September 30, 2018 through the maturity of the Line of Credit. As of September 30, 2018 , we were in compliance with the financial covenants of the Line of Credit. Further, we had no amounts outstanding and were able to borrow up to $30.0 million under the Line of Credit.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We lease our offices under operating leases, which expire at various dates through 2022. Our primary operating lease commitments at September 30, 2018 are related to our corporate headquarters in Santa Clara, California. We have additional offices in California, Oregon and New York in the United States and internationally in India, Israel and Berlin. We recognize rent expense on a straight-line basis over the lease period. 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 rent expense over the lease term. Rental expense, net of sublease income, was approximately $0.9 million and $2.2 million during the three and nine months ended September 30, 2018 , respectively, and approximately $0.6 million and $2.0 million during the three and nine months ended September 30, 2017 , respectively. 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. 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 consolidated financial position, results of operations, or cash flows. However, our determination of whether a claim will proceed to litigation cannot be made 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 any of these actions, including a judgment or settlement, may cause a material adverse effect on our future business, operating results, and/or financial condition.

Guarantees and Indemnifications

Guarantees and Indemnifications	9 Months Ended
	Sep. 30, 2018
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 immaterial. We have not recorded any liabilities for these agreements as of September 30, 2018 .

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stockholders' Equity	Stockholders' Equity In conjunction with our April 2018 offering of convertible senior notes, we repurchased 983,284 shares of our common stock at an average price per share of $20.34 . Share-based Compensation Expense Total share-based compensation expense recorded for employees and non-employees, is as follows (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Cost of revenues $ 106 $ 73 $ 303 $ 228 Research and development 4,528 3,706 12,190 10,334 Sales and marketing 1,675 1,261 4,994 3,588 General and administrative 7,509 5,051 20,016 13,318 Total share-based compensation expense $ 13,818 $ 10,091 $ 37,503 $ 27,468 There was no capitalized share-based compensation expense as of September 30, 2018 or 2017 . RSU and PSU Activity Activity for RSUs and PSUs is as follows: RSUs and PSUs Outstanding Number of RSUs and PSUs Outstanding Weighted Average Grant Date Fair Value Balance at December 31, 2017 14,335,115 $ 6.78 Granted 3,452,774 21.35 Released (5,249,303 ) 6.48 Canceled (1,521,060 ) 6.95 Balance at September 30, 2018 11,017,526 $ 11.47 As of September 30, 2018 , our total unrecognized share-based compensation expense related to RSUs and PSUs was approximately $74.8 million , which will be recognized over the remaining weighted-average vesting period of approximately 1.6 years .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes 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 state and foreign income tax expense. We recorded an income tax provision of approximately $0.6 million and $2.0 million during the three and nine months ended September 30, 2017 , respectively, primarily due to state and foreign income tax expense and federal tax expense related to acquired indefinite lived intangible assets. On December 22, 2017 , Staff Accounting Bulletin No. 118 (SAB 118) was issued to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act (Tax Act). In accordance with SAB 118, as of September 30, 2018 , we have not yet completed our accounting for the tax effects of the enactment of the Tax Act. Our estimate of the effects the Tax Act has not materially changed from the amounts recorded during the year ended December 31, 2017. We will continue to analyze certain aspects of the Tax Act and the newly issued Internal Revenue Service proposed regulations and we expect future proposed and final regulations may continue to impact and refine our estimates.

Restructuring Charges

Restructuring Charges	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring Charges 2017 Restructuring Plan In January 2017, we entered into a strategic partnership with NRCCUA where they will assume responsibility for managing, renewing, and maintaining our existing university contracts and become the exclusive reseller of our digital Enrollment Marketing services for colleges and universities. As a result of this strategic partnership, approximately 50 employees in China and the United States supporting the sales and account support functions of our Enrollment Marketing offering were terminated. Costs incurred to date are expected to be fully paid within 4 months. 2015 Restructuring Plan Restructuring charges of $0.2 million recorded during the nine months ended September 30, 2018 primarily related to our subtenant filing for bankruptcy and exiting our leased office. Costs incurred to date are expected to be fully paid by 2021. The following table summarizes the activity related to the accrual for restructuring charges (credits) (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, 2017 $ — $ — $ 306 $ 306 Restructuring charges (credits) 941 148 (42 ) 1,047 Cash payments (897 ) (128 ) (43 ) (1,068 ) Write-offs — (20 ) — (20 ) Balance at December 31, 2017 44 — 221 265 Restructuring charges 82 13 157 252 Cash payments (96 ) (13 ) (147 ) (256 ) Write-offs — — (18 ) (18 ) Balance at September 30, 2018 $ 30 $ — $ 213 $ 243 As of September 30, 2018 , the $0.2 million liability was comprised of a short-term accrual of $0.1 million included within accrued liabilities and a long-term accrual of $0.1 million included within other liabilities on our condensed consolidated balance sheet.

Related-Party Transactions

Related-Party Transactions	9 Months Ended
	Sep. 30, 2018
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, 2018 , we had purchases of $0.6 million and $2.8 million , respectively, and during the three and nine months ended September 30, 2017 , we had purchases of $0.8 million and $2.6 million , respectively, 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 no revenues during the three and nine months ended September 30, 2017 from Adobe. We had $0.2 million in payables as of September 30, 2018 and December 31, 2017 to Adobe. We had $0.5 million in accounts receivable as of September 30, 2018 and an immaterial amount of accounts receivable as of December 31, 2017 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, 2018 , we had purchases of $3.8 million and $10.3 million , respectively, and during the three and nine months ended September 30, 2017 , we had purchases of $4.7 million and $9.5 million , respectively, from Cengage. We had $1.2 million and $3.2 million of revenues during the three and nine months ended September 30, 2018 , respectively, and $1.2 million and $1.8 million of revenues during the three and nine months ended September 30, 2017 , respectively, from Cengage. We had $2.0 million and $0.1 million in payables as of September 30, 2018 and December 31, 2017 , respectively, to Cengage. We had an immaterial amount of outstanding accounts receivable as of September 30, 2018 and $0.3 million in outstanding accounts receivable as of December 31, 2017 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, 2018 , we incurred payment processing fees of $0.4 million and $1.0 million , respectively, and during the three and nine months ended September 30, 2017 , we incurred payment processing fees of $0.3 million and $0.8 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 months ended September 30, 2018 , we had purchases of $0.1 million of services from Synack.

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event On October 29, 2018 , we completed an investment of $10.0 million in WayUp, Inc., a US-based job site and mobile application for college students and recent graduates. Our investment will be accounted for under the cost method and included in other assets on our condensed consolidated balance sheet.

Background and Basis of Prese_2

Background and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated balance sheet as of September 30, 2018 , the condensed consolidated statements of operations and the condensed consolidated statements of comprehensive loss for the three and nine months ended September 30, 2018 and 2017 , the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017 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, 2018 , our results of operations for the three and nine months ended September 30, 2018 and 2017 , and cash flows for the nine months ended September 30, 2018 and 2017 . Our results of operations and cash flows for the nine months ended September 30, 2018 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, 2017 as 2017 . 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, 2017 (the Annual Report on Form 10-K) filed with the U.S. Securities and Exchange Commission (SEC). We have changed the caption on our condensed consolidated statements of operations from “technology and development” to “research and development.” This change does not impact any current or previously reported amounts. Except for our policies on revenue recognition, deferred revenue 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.
Revenue Recognition and Deferred Revenue	Revenue Recognition and Deferred Revenue We recognize revenues from our Chegg Services and Required Materials offerings when control of the 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. We determine revenue recognition through the following steps: • Identification of the contract, or contracts, with a customer • Identification of the performance obligations in the contract • Determination of the transaction price • Allocation of the transaction price to the performance obligations in the contract • Recognition of revenue when, or as, we satisfy a performance obligation We generate revenues from our Chegg Services product line including our Chegg Study service, our Chegg Writing service, our Chegg Tutors service, Test Prep, through our partnership with Kaplan Test Prep (Kaplan), Internship services, Brand Partnership services that we offer to brands and Enrollment Marketing services to colleges, through our strategic partnership with the National Research Center for College and University Admissions (NRCCUA). Chegg Services are offered to students through weekly, monthly or annual subscriptions, and we primarily recognize revenues ratably over the respective subscription period. Enrollment Marketing services and Brand Partnership services are offered either on a subscription or on an a la carte basis. Revenues are recognized ratably or as earned over the subscription service period, generally one year. Revenues from Enrollment Marketing services or Brand Partnership services delivered on an a la carte basis, without a subscription, are recognized when delivery of the respective lead or service has occurred. Historically, under previous revenue recognition guidance, revenue recognition was delayed for certain contracts with extended payment terms. For these services, we bill the customer at the inception, over the term of the customer arrangement or as the services are performed. Upon satisfactory assessment of creditworthiness, we generally grant credit to our Enrollment Marketing and Brand Partnership customers with normal credit terms, typically 30 days. Some of our customer arrangements for Brand Partnership and Enrollment Marketing services include multiple performance obligations. We have determined these performance obligations qualify as distinct performance obligations, as the customer can benefit from the service on its own or together with other resources that are readily available to the customer and our promise to transfer the service is separately identifiable from other promises in the contract. For these arrangements that contain distinct performance obligations, we allocate the transaction price based on the relative standalone selling price method by comparing the standalone selling price (SSP) of each distinct performance obligation to the total value of the contract. We determine the SSP based on our historical pricing and discounting practices for the distinct performance obligation when sold separately. If the SSP is not directly observable, we estimate the SSP by considering information such as market conditions, and information about the customer. Additionally, we limit the amount of revenues recognized for delivered promises to the amount that is not contingent on future delivery of services or other future performance obligations. We also generate revenues from our Required Materials product line including revenue share earned on print textbooks for rental or sale transactions, owned by Ingram and other partners, which are recognized immediately when a book ships to the student. Revenues from the rental or sale of eTextbooks is recognized ratably over the contractual period, generally two to five months, or at time of the sale, respectively. Our strategic partnership with Ingram includes an amount of variable consideration in addition to a fixed revenue share that we earn. This variable consideration can either increase or decrease the total transaction price depending on the nature of the variable consideration. Under the new revenue recognition guidance, we estimate the amount of variable consideration that we will earn at the inception of the contract, adjusted during each period, and include an estimated amount each period as opposed to the contractual amount earned under the previous revenue recognition guidance. For sales of third party products, we evaluate whether we are acting as a principal or an agent, and therefore would record the gross sales amount as revenues and related costs or the net amount earned as a revenue share from the sale of third party products. Our determination is based on our evaluation of whether we control the specified goods or services prior to transferring them to the customer. For our strategic partnership with Ingram and our agreements with other textbook publishers, we have concluded that we do not control the use of the print textbooks, and therefore record net revenue only for the revenue share we earn upon the shipment of a print textbook to a student. For the rental or sale of eTextbooks, we have concluded that we control the service, therefore we recognize revenue and cost of revenue on a gross basis ratably over the term the student has access to the eTextbook. Revenues are presented net of sales tax collected from customers to be remitted to governmental authorities and net of allowances for estimated cancellations and customer returns, which are based on historical data. Customer refunds from cancellations and returns are recorded as a reduction to revenues. Contract assets are contained within other current assets on our condensed consolidated balance sheets. Contract assets represent the goods or services that we have transferred to a customer before invoicing the customer. Contract receivables are contained within accounts receivable, net on our condensed consolidated balance sheets and represent unconditional consideration that will be received solely due to the passage of time. Contract liabilities are contained within deferred revenue on our condensed consolidated balance sheets. Deferred revenue primarily consists of advanced payments from students related to rental and subscription performance obligations that have not been satisfied, Brand Partnership and Enrollment Marketing performance obligations that have yet to be satisfied, and the estimated variable consideration as a result of our strategic partnership with Ingram. Deferred revenue related to rental and subscription performance obligations is recognized as revenues ratably over the term for subscriptions or when the services are provided and all other revenue recognition criteria have been met. Deferred revenue related to variable consideration is recognized as revenues during each reporting period based on the estimated amount we believe we will earn over the life of the contract.
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 including variable consideration, recoverability of accounts receivable, fair value of debt and equity components related to our convertible senior notes, restructuring charges, share-based compensation expense including estimated forfeitures, accounting for income taxes, useful lives assigned to long-lived assets for depreciation and amortization, valuation of goodwill and long-lived assets, and the valuation of acquired intangible assets. 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 August 2018, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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, and we are currently in the process of evaluating the impact of this guidance. The FASB has issued three ASU's related to Accounting Standards Codification (ASC) 842. 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). ASU 2016-02 requires an entity to recognize a right-of-use 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. ASC 842 allows for 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 plan to elect this package of transition practical expedients. ASU 2018-10 provides additional updates and corrections to topics included within ASC 842 based on the FASB's interactions with stakeholders. ASU 2018-11 allows for a modified retrospective adoption with a cumulative-effect adjustment to the opening balance of accumulated deficit in the period of adoption. We plan to elect this transition method of adoption. Early adoption is permitted and the guidance is effective for annual periods beginning after December 15, 2018. We plan to adopt the guidance on January 1, 2019. At this time, we do not know the quantitative impact of adopting ASU 2016-02; however, we initially believe that this will only have an impact on our condensed consolidated balance sheet and little to no impact to our condensed consolidated statement of operations. We will continue to evaluate as we near our adoption date. 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 In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting . ASU 2018-07 expands the scope of Topic 718, Compensation—Stock Compensation to include share-based payment transactions for acquiring goods and services from non-employees. These awards are measured at the grant-date fair value of the equity instruments that an entity is obligated to issue when the good has been delivered or the service has been rendered and any other conditions necessary to earn the right to benefit from the instruments have been satisfied. The guidance is effective for annual periods after December 15, 2018, with early adoption permitted, and the guidance requires a modified retrospective application to awards that have not been settled as of the adoption date. We have elected to early adopt this guidance during the second quarter of 2018 and our adoption did not result in an adjustment to the opening balance of accumulated deficit. In February 2018, the FASB issued ASU No. 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . ASU 2018-02 allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. We adopted the guidance on January 1, 2018 recording an immaterial reclassification from accumulated other comprehensive income (loss) to the opening balance of accumulated deficit. In January 2017, the FASB issued ASU No. 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment . ASU 2017-04 eliminates step 2 from the annual goodwill impairment test no longer requiring the comparison of the implied fair value of a reporting unit's goodwill with the carrying amount of goodwill. We early adopted the guidance to simplify our goodwill impairment test, with a prospective application on January 1, 2018 and will apply the guidance starting with our 2018 annual goodwill impairment assessment. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business . ASU 2017-01 clarifies the definition of a business to assist entities with evaluating whether a transaction should be accounted for as acquisitions of assets or businesses. We adopted the guidance with a prospective application on January 1, 2018. We will analyze the clarified definition of a business to determine whether transactions from our application date should be accounted for as an asset acquisition or business combination under the new guidance. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . ASU 2016-18 requires an entity to explain the change during a period in restricted cash equivalents on the condensed consolidated statements of cash flows and include such amounts when reconciling beginning-of-period and end-of-period total amounts shown on the condensed consolidated statements of cash flows. We adopted the guidance with a retrospective application on January 1, 2018 and have adjusted our beginning-of-period and end-of-period amounts on our condensed consolidated statement of cash flows to include restricted cash with the change in restricted cash included within the other assets line on our condensed consolidated statement of cash flows. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . ASU 2016-01 requires entities to measure equity investments at fair value and recognize any changes in fair value within the condensed consolidated statement of operations. We have a strategic investment of $3.0 million recorded in other assets on our condensed consolidated balance sheets that falls under this guidance update. The guidance provides for electing a measurement alternative for equity investments that do not have readily determinable fair values. We have elected the measurement alternative for our strategic investment as there is not a readily determinable fair value, which we will apply to our strategic investment starting with our adoption date of January 1, 2018. This investment will be measured at cost, less any impairment, plus or minus adjustments resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer , with any changes in the value of the investment recorded within the condensed consolidated statement of operations. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, as amended (Topic 606) (ASC 606), which changes the way we recognize revenue and significantly expands the disclosure requirements for revenue arrangements. We adopted ASU 2014-09 under the modified retrospective application, recording the cumulative effect of adoption as an adjustment to the opening balance of accumulated deficit on our adoption date of January 1, 2018. We have not adjusted previously reported amounts. Adoption of the new standard resulted in changes to our accounting policies for revenue recognition, and trade and other receivables. See Note 2 for more information.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing 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, warrants, shares related to convertible senior notes, restricted stock units (RSUs), and performance-based restricted stock units (PSUs), 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)

Revenues (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table sets 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 Change 2018 2017 (1) $ % Chegg Services $ 54,201 $ 39,475 $ 14,726 37 % Required Materials 20,036 23,165 (3,129 ) (14 )% Total net revenues $ 74,237 $ 62,640 $ 11,597 19 % Nine Months Ended Change 2018 2017 (1) $ % Chegg Services $ 172,327 $ 125,210 $ 47,117 38 % Required Materials 53,081 56,349 (3,268 ) (6 )% Total net revenues $ 225,408 $ 181,559 $ 43,849 24 % (1) As noted above, prior period amounts have not been adjusted under the modified retrospective method.
Schedule of Accounts Receivable	The following table presents our accounts receivable, net and deferred revenue balances (in thousands, except percentages): Change September 30, 2018 December 31, 2017 $ % Accounts receivable, net $ 8,620 $ 10,855 $ (2,235 ) (21 )% Deferred revenue $ 25,281 $ 13,440 $ 11,841 88 %

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of historical basic and diluted net loss per share (in thousands, except per share amounts): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Numerator: Net loss $ (13,709 ) $ (11,516 ) $ (20,235 ) $ (23,942 ) Denominator: Weighted average shares used to compute net loss per share, basic and diluted 114,184 103,041 112,621 97,008 Net loss per share, basic and diluted $ (0.12 ) $ (0.11 ) $ (0.18 ) $ (0.25 )
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 Nine Months Ended 2018 2017 2018 2017 Options to purchase common stock 3,961 2 4,282 3,167 RSUs and PSUs 7,479 49 8,075 137 Shares related to convertible senior notes 1,221 — — — Employee stock purchase plan 17 — 12 — Warrants to purchase common stock — — — 200 Total common stock equivalents 12,678 51 12,369 3,504

Cash and Cash Equivalents, an_2

Cash and Cash Equivalents, and Investment (Tables)	9 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Investments	The following table shows our cash and cash equivalents, and investments’ cost, net unrealized loss and fair value as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Cost Net Unrealized Loss Fair Value Cost Net Unrealized Loss Fair Value Cash and cash equivalents: Cash $ 340,933 $ — $ 340,933 $ 98,370 $ — $ 98,370 Money market funds 7,017 — 7,017 5,358 — 5,358 Commercial paper 31,071 (1 ) 31,070 22,729 — 22,729 Total cash and cash equivalents $ 379,021 $ (1 ) $ 379,020 $ 126,457 $ — $ 126,457 Short-term investments: Commercial paper $ 29,461 $ (1 ) $ 29,460 $ 38,850 $ (27 ) $ 38,823 Corporate securities 40,658 (103 ) 40,555 23,001 (43 ) 22,958 U.S. treasury securities 10,891 (8 ) 10,883 19,978 (17 ) 19,961 Total short-term investments $ 81,010 $ (112 ) $ 80,898 $ 81,829 $ (87 ) $ 81,742 Long-term investments: Corporate securities $ 13,343 $ (1 ) $ 13,342 $ 20,405 $ (100 ) $ 20,305 U.S. treasury securities 1,626 (7 ) 1,619 — — — Total long-term investments $ 14,969 $ (8 ) $ 14,961 $ 20,405 $ (100 ) $ 20,305
Schedule of Available-for-sale Securities Reconciliation	The cost and fair value of available-for-sale investments as of September 30, 2018 by contractual maturity were as follows (in thousands): Cost Fair Value Due in 1 year or less $ 112,081 $ 111,968 Due in 1-2 years 14,969 14,961 Investments not due at a single maturity date 7,017 7,017 Total $ 134,067 $ 133,946

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2018 and December 31, 2017 are classified based on the valuation technique level in the tables below (in thousands): September 30, 2018 Total Quoted Prices Significant Assets: Cash equivalents: Money market funds $ 7,017 $ 7,017 $ — Commercial paper 31,070 — 31,070 Short-term investments: Commercial paper 29,460 — 29,460 Corporate securities 40,555 — 40,555 U.S. treasury securities 10,883 10,883 — Long-term investments: Corporate securities 13,342 — 13,342 U.S. treasury securities 1,619 1,619 — Total assets measured and recorded at fair value $ 133,946 $ 19,519 $ 114,427 December 31, 2017 Total Quoted Prices Significant Assets: Cash equivalents: Money market funds $ 5,358 $ 5,358 $ — Commercial paper 22,729 — 22,729 Short-term investments: — Commercial paper 38,823 — 38,823 Corporate securities 22,958 — 22,958 U.S. treasury securities 19,961 19,961 — Long-term corporate securities 20,305 — 20,305 Total assets measured and recorded at fair value $ 130,134 $ 25,319 $ 104,815
Fair Value Measurements, Nonrecurring	The carrying amounts and estimated fair values of financial instruments not recorded at fair value as of September 30, 2018 are as follows (in thousands): September 30, 2018 Carrying Amount Estimated Fair Value Convertible senior notes, net $ 280,132 $ 411,143

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Schedule Of Fair Value Of Consideration	The acquisition date fair value of the purchase consideration for the above transactions consisted of the following (in thousands): Initial cash consideration $ 29,980 Escrow 5,820 Net working capital adjustment (916 ) Fair value of purchase consideration $ 34,884
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table presents the total allocation of purchase consideration recorded in our condensed consolidated balance sheets as of the acquisition date (in thousands): Cash $ 234 Accounts receivable 302 Other acquired assets 151 Acquired intangible assets: Trade name 140 Domain names 180 Non-compete agreements 220 Developed technology 5,790 Content library 5,220 Total acquired intangible assets 11,550 Total identifiable assets acquired 12,237 Liabilities assumed (2,133 ) Net identifiable assets acquired 10,104 Goodwill 24,780 Total fair value of purchase consideration $ 34,884

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill consists of the following (in thousands): Nine Months Ended Year Ended December 31, 2017 Beginning balance $ 125,272 $ 116,239 Additions due to acquisitions 24,780 9,024 Foreign currency translation adjustment (290 ) 9 Ending balance $ 149,762 $ 125,272
Finite-Lived Intangible Assets	Intangible assets as of September 30, 2018 and December 31, 2017 consist of the following (in thousands, except the weighted-average amortization period in months): September 30, 2018 Weighted-Average Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Developed technologies 71 $ 31,667 $ (12,655 ) $ 19,012 Customer lists 47 9,970 (6,505 ) 3,465 Trade names 44 6,113 (4,542 ) 1,571 Non-compete agreements 31 2,018 (1,668 ) 350 Master service agreements 21 1,030 (1,030 ) — Indefinite-lived trade name — 3,600 — 3,600 Foreign currency translation adjustment — (185 ) — (185 ) Total intangible assets 61 $ 54,213 $ (26,400 ) $ 27,813 December 31, 2017 Weighted-Average Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Developed technologies 70 $ 20,657 $ (10,220 ) $ 10,437 Customer lists 47 9,970 (5,480 ) 4,490 Trade names 46 5,793 (3,465 ) 2,328 Non-compete agreements 30 1,798 (1,506 ) 292 Master service agreements 21 1,030 (1,030 ) — Indefinite-lived trade name — 3,600 — 3,600 Foreign currency translation adjustment — 6 — 6 Total intangible assets 57 $ 42,854 $ (21,701 ) $ 21,153
Indefinite-lived Intangible Assets	Intangible assets as of September 30, 2018 and December 31, 2017 consist of the following (in thousands, except the weighted-average amortization period in months): September 30, 2018 Weighted-Average Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Developed technologies 71 $ 31,667 $ (12,655 ) $ 19,012 Customer lists 47 9,970 (6,505 ) 3,465 Trade names 44 6,113 (4,542 ) 1,571 Non-compete agreements 31 2,018 (1,668 ) 350 Master service agreements 21 1,030 (1,030 ) — Indefinite-lived trade name — 3,600 — 3,600 Foreign currency translation adjustment — (185 ) — (185 ) Total intangible assets 61 $ 54,213 $ (26,400 ) $ 27,813 December 31, 2017 Weighted-Average Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Developed technologies 70 $ 20,657 $ (10,220 ) $ 10,437 Customer lists 47 9,970 (5,480 ) 4,490 Trade names 46 5,793 (3,465 ) 2,328 Non-compete agreements 30 1,798 (1,506 ) 292 Master service agreements 21 1,030 (1,030 ) — Indefinite-lived trade name — 3,600 — 3,600 Foreign currency translation adjustment — 6 — 6 Total intangible assets 57 $ 42,854 $ (21,701 ) $ 21,153
Estimated Future Amortization Expense Related to Intangible Assets	As of September 30, 2018 , the estimated future amortization expense related to our finite-lived intangible assets is as follows (in thousands): Remaining three months of 2018 $ 1,811 2019 6,448 2020 4,816 2021 3,423 2022 2,943 Thereafter 4,772 Total $ 24,213

Convertible Senior Notes (Table

Convertible Senior Notes (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule Of Net Proceeds From Debt Issuance	The total net proceeds from the notes are as follows (in thousands): Principal amount $ 345,000 Less initial purchasers’ discount (8,625 ) Less other issuance costs (757 ) Net proceeds $ 335,618
Schedule of Debt	The net carrying amount of the liability component of the notes is as follows (in thousands): As of September 30, 2018 Principal $ 345,000 Unamortized debt discount (57,976 ) Unamortized issuance costs (6,892 ) Net carrying amount $ 280,132 The net carrying amount of the equity component of the notes is as follows (in thousands): As of September 30, 2018 Debt discount for conversion option $ 64,193 Issuance costs (1,749 ) Net carrying amount $ 62,444
Schedule Of Interest Expense Recognized	The following table sets forth the total interest expense recognized related to the notes (in thousands): Three Months Ended Nine Months Ended Contractual interest expense $ 218 $ 428 Amortization of debt discount 3,160 6,217 Amortization of issuance costs 377 741 Total interest expense $ 3,755 $ 7,386

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [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 Nine Months Ended 2018 2017 2018 2017 Cost of revenues $ 106 $ 73 $ 303 $ 228 Research and development 4,528 3,706 12,190 10,334 Sales and marketing 1,675 1,261 4,994 3,588 General and administrative 7,509 5,051 20,016 13,318 Total share-based compensation expense $ 13,818 $ 10,091 $ 37,503 $ 27,468
Summary of Restricted Stock Unit Activity	Activity for RSUs and PSUs is as follows: RSUs and PSUs Outstanding Number of RSUs and PSUs Outstanding Weighted Average Grant Date Fair Value Balance at December 31, 2017 14,335,115 $ 6.78 Granted 3,452,774 21.35 Released (5,249,303 ) 6.48 Canceled (1,521,060 ) 6.95 Balance at September 30, 2018 11,017,526 $ 11.47

Restructuring Charges (Tables)

Restructuring Charges (Tables)	9 Months Ended
	Sep. 30, 2018
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 (credits) (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, 2017 $ — $ — $ 306 $ 306 Restructuring charges (credits) 941 148 (42 ) 1,047 Cash payments (897 ) (128 ) (43 ) (1,068 ) Write-offs — (20 ) — (20 ) Balance at December 31, 2017 44 — 221 265 Restructuring charges 82 13 157 252 Cash payments (96 ) (13 ) (147 ) (256 ) Write-offs — — (18 ) (18 ) Balance at September 30, 2018 $ 30 $ — $ 213 $ 243

Background and Basis of Prese_3

Background and Basis of Presentation (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Apr. 30, 2018
Cost-method Investments | Other Assets
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Investments	$ 3,000,000
Chegg Services
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue recognition, subscription service period	1 year
Minimum | Required Materials
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue recognition, textbook rental or sale, contractual period	2 months
Maximum | Required Materials
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue recognition, textbook rental or sale, contractual period	5 months
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
Interest rate, stated percentage		0.25%

Revenues (Details)

Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total net revenues	$ 74,237	$ 62,640	$ 225,408	$ 181,559
Change in total net revenues	$ 11,597		$ 43,849
Change in total net revenues, percent	19.00%		24.00%
Aggregate amount of unsatisfied performance obligations	$ 29,000		$ 29,000
Contract with customer, liability, revenue recognized	10,800		11,700
Accounts receivable	8,620		8,620		$ 10,855
Deferred revenue	25,281		25,281		$ 13,440
Change in accounts receivable			$ (2,235)
Change in accounts receivable, percent			(21.00%)
Change in deferred revenue			$ 11,841
Change in deferred revenue, percent			88.00%
Enrollment Marketing
Disaggregation of Revenue [Line Items]
Change in deferred revenue	1,000		$ 2,100
Chegg Services
Disaggregation of Revenue [Line Items]
Total net revenues	54,201	39,475	172,327	125,210
Change in total net revenues	$ 14,726		$ 47,117
Change in total net revenues, percent	37.00%		38.00%
Required Materials
Disaggregation of Revenue [Line Items]
Total net revenues	$ 20,036	$ 23,165	$ 53,081	$ 56,349
Change in total net revenues	$ (3,129)		$ (3,268)
Change in total net revenues, percent	(14.00%)		(6.00%)

Net Loss Per Share - Computatio

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, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss	$ (13,709)	$ (11,516)	[1]	$ (20,235)	$ (23,942)	[1]
Denominator:
Weighted average shares used to compute net loss per share, basic and diluted (in shares)	114,184	103,041		112,621	97,008
Net loss per share, basic and diluted (in dollars per share)	$ (0.12)	$ (0.11)		$ (0.18)	$ (0.25)
[1]	Adjusted to reflect the adoption of ASU 2016-18. See Note 1 for more information.

Net Loss Per Share - Shares Exc

Net Loss Per Share - Shares Excluded From Computation Of Diluted Net Loss Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	12,678	51	12,369	3,504
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	3,961	2	4,282	3,167
RSUs and PSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	7,479	49	8,075	137
Shares related to convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	1,221	0	0	0
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	17	0	12	0
Warrants to purchase common stock | Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	0	0	0	200

Cash and Cash Equivalents, an_3

Cash and Cash Equivalents, and Investment - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Restricted cash	$ 0.7	$ 0.5
Other Assets | Equity Investments
Schedule of Investments [Line Items]
Investments	$ 3

Cash and Cash Equivalents, an_4

Cash and Cash Equivalents, and Investment - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Cost	$ 134,067
Fair Value	133,946
Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Cost	379,021	$ 126,457
Net Unrealized Loss	(1)	0
Fair Value	379,020	126,457
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Cost	81,010	81,829
Net Unrealized Loss	(112)	(87)
Fair Value	80,898	81,742
Total long-term investments
Debt Securities, Available-for-sale [Line Items]
Cost	14,969	20,405
Net Unrealized Loss	(8)	(100)
Fair Value	14,961	20,305
Corporate securities | Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Cost	40,658	23,001
Net Unrealized Loss	(103)	(43)
Fair Value	40,555	22,958
Corporate securities | Total long-term investments
Debt Securities, Available-for-sale [Line Items]
Cost	13,343	20,405
Net Unrealized Loss	(1)	(100)
Fair Value	13,342	20,305
Commercial paper | Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Cost	29,461	38,850
Net Unrealized Loss	(1)	(27)
Fair Value	29,460	38,823
U.S. treasury securities | Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Cost	10,891	19,978
Net Unrealized Loss	(8)	(17)
Fair Value	10,883	19,961
U.S. treasury securities | Total long-term investments
Debt Securities, Available-for-sale [Line Items]
Cost	1,626	0
Net Unrealized Loss	(7)	0
Fair Value	1,619	0
Cash | Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Cost	340,933	98,370
Net Unrealized Loss	0	0
Fair Value	340,933	98,370
Money market funds | Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Cost	7,017	5,358
Net Unrealized Loss	0	0
Fair Value	7,017	5,358
Commercial paper | Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Cost	31,071	22,729
Net Unrealized Loss	(1)	0
Fair Value	$ 31,070	$ 22,729

Cash and Cash Equivalents, an_5

Cash and Cash Equivalents, and Investment - Contractual Maturity (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Cash and Cash Equivalents [Abstract]
Due in 1 year or less, Cost	$ 112,081
Due in 1-2 years, Cost	14,969
Investments not due at a single maturity date, Cost	7,017
Cost	134,067
Due in 1 year or less, Fair Value	111,968
Due in 1-2 years, Fair Value	14,961
Investments not due at a single maturity date, Fair Value	7,017
Total, Fair Value	$ 133,946
Weighted average maturity	5 months

Fair Value Measurement (Details

Fair Value Measurement (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 80,898	$ 81,742
Long-term investments	14,961	20,305
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	133,946	130,134
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	19,519	25,319
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	114,427	104,815
Commercial paper | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	29,460	38,823
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	29,460	38,823
Corporate securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	40,555	22,958
Long-term investments	13,342	20,305
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	40,555	22,958
Long-term investments	13,342	20,305
U.S. treasury securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	10,883	19,961
Long-term investments	1,619
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	10,883	19,961
Long-term investments	1,619
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
Money market funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	7,017	5,358
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	7,017	5,358
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	31,070	22,729
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	$ 31,070	$ 22,729

Fair Value Measurement - Debt (

Fair Value Measurement - Debt (Details) - Senior Notes $ in Thousands	Sep. 30, 2018USD ($)
Carrying Amount | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes, net	$ 280,132
Estimated Fair Value | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior notes, net	411,143
0.25% Convertible Senior Notes Due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unamortized debt discount	57,976
Unamortized issuance costs	$ 6,892

Acquisitions (Details)

Acquisitions (Details) - USD ($) $ in Thousands	Jul. 02, 2018	May 15, 2018	Jul. 02, 2018	Sep. 30, 2018	Sep. 30, 2018
StudyBlue, Inc.
Business Acquisition [Line Items]
Escrow	$ 3,300
Fair value of purchase consideration	$ 20,400
WriteLab, Inc.
Business Acquisition [Line Items]
Escrow		$ 2,600
Fair value of purchase consideration		14,500
Contingent payments		$ 5,000
Contingent consideration, liability				$ 600	$ 600
Acquisition related costs				$ 600	$ 1,000
WriteLab, Inc. and StudyBlue, Inc.
Business Acquisition [Line Items]
Initial cash consideration			$ 29,980
Escrow			5,820
Net working capital adjustment			(916)
Fair value of purchase consideration			$ 34,884

Acquisitions - Assets Acquired

Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2018	May 15, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 149,762		$ 125,272	$ 116,239
WriteLab, Inc.
Business Acquisition [Line Items]
Cash		$ 234
Accounts receivable		302
Other acquired assets		151
Total acquired intangible assets		11,550
Total identifiable assets acquired		12,237
Liabilities assumed		(2,133)
Net identifiable assets acquired		10,104
Goodwill		24,780
Total fair value of purchase consideration		34,884
Trade names | WriteLab, Inc.
Business Acquisition [Line Items]
Total acquired intangible assets		140
Domain names | WriteLab, Inc.
Business Acquisition [Line Items]
Total acquired intangible assets		180
Non-compete agreements | WriteLab, Inc.
Business Acquisition [Line Items]
Total acquired intangible assets		220
Developed technologies | WriteLab, Inc.
Business Acquisition [Line Items]
Total acquired intangible assets		5,790
Content library | WriteLab, Inc.
Business Acquisition [Line Items]
Total acquired intangible assets		$ 5,220

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Beginning balance	$ 125,272	$ 116,239
Additions due to acquisitions	24,780	9,024
Foreign currency translation adjustment	(290)	9
Ending balance	$ 149,762	$ 125,272

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Finite-lived and Indefinite-lived Intangibe Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	61 months	57 months
Accumulated Amortization	$ (26,400)	$ (21,701)
Net Carrying Amount	24,213
Indefinite-lived trade name	3,600	3,600
Foreign currency translation adjustment	(185)	6
Total intangible assets, gross carrying amount	54,213	42,854
Intangible assets, net	$ 27,813	$ 21,153
Developed technologies
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	71 months	70 months
Gross Carrying Amount	$ 31,667	$ 20,657
Accumulated Amortization	(12,655)	(10,220)
Net Carrying Amount	$ 19,012	$ 10,437
Customer lists
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	47 months	47 months
Gross Carrying Amount	$ 9,970	$ 9,970
Accumulated Amortization	(6,505)	(5,480)
Net Carrying Amount	$ 3,465	$ 4,490
Trade names
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	44 months	46 months
Gross Carrying Amount	$ 6,113	$ 5,793
Accumulated Amortization	(4,542)	(3,465)
Net Carrying Amount	$ 1,571	$ 2,328
Non-compete agreements
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	31 months	30 months
Gross Carrying Amount	$ 2,018	$ 1,798
Accumulated Amortization	(1,668)	(1,506)
Net Carrying Amount	$ 350	$ 292
Master service agreements
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	21 months	21 months
Gross Carrying Amount	$ 1,030	$ 1,030
Accumulated Amortization	(1,030)	(1,030)
Net Carrying Amount	$ 0	$ 0

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Acquisition-Related Intangible Assets
Finite Lived Intangible Assets [Line Items]
Amortization expense of acquisition related to acquired intangible assets	$ 1.8	$ 1.4	$ 4.7	$ 4.1

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Estimated Future Amortization Expense Related to Intangible Assets (Details) $ in Thousands	Sep. 30, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining three months of 2018	$ 1,811
2,019	6,448
2,020	4,816
2,021	3,423
2,022	2,943
Thereafter	4,772
Net Carrying Amount	$ 24,213

Convertible Senior Notes - Conv

Convertible Senior Notes - Convertible Senior Notes (Details)	Jun. 30, 2018USD ($)	Apr. 30, 2018USD ($)day$ / sharesshares	Sep. 30, 2018USD ($)$ / shares	Sep. 30, 2017USD ($)	[1]	Dec. 31, 2018$ / shares
Debt Instrument [Line Items]
Net proceeds			$ 335,618,000	$ 0
Senior Notes | 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Face value		$ 345,000,000	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		0.037051
Equity component		$ 64,200,000	$ 62,444,000
Debt issuance costs		(9,400,000)
Debt instrument, remaining useful life			4 years 7 months 6 days
Share price (in dollars per share) | $ / shares			$ 28.43
Principal	$ 363,900,000
Debt instrument, if-converted value in excess of principal		$ (18,900,000)
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 | 0.25% 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 | 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Debt issuance costs		(1,700,000)
Capped Call | Senior Notes | 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Net proceeds		$ 39,200,000
Conversion price | $ / shares		$ 26.95
Shares covered by capped call transactions (in shares) | shares		12,801,260
Scenario, Forecast | Capped Call | Senior Notes | 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Conversion price | $ / shares						$ 40.68
[1]	Adjusted to reflect the adoption of ASU 2016-18. See Note 1 for more information.

Convertible Senior Notes - Net

Convertible Senior Notes - Net Carrying Amount (Details) - USD ($)	Sep. 30, 2018	Apr. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Net carrying amount	$ 280,132,000		$ 0
Senior Notes | 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Principal	345,000,000	$ 345,000,000
Unamortized debt discount	(57,976,000)
Unamortized issuance costs	(6,892,000)
Net carrying amount	280,132,000
Debt discount for conversion option	64,193,000
Issuance costs	(1,749,000)
Net carrying amount	$ 62,444,000	$ 64,200,000

Convertible Senior Notes - Inte

Convertible Senior Notes - Interest Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Debt Instrument [Line Items]
Contractual interest expense		$ 428
Amortization of debt discount		6,217
Amortization of issuance costs		741
Total interest expense		$ 7,386
Senior Notes | 0.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Contractual interest expense	$ 218
Amortization of debt discount	3,160
Amortization of issuance costs	377
Total interest expense	$ 3,755

Revolving Line of Credit (Detai

Revolving Line of Credit (Details) - Revolving Credit Facility - USD ($)	3 Months Ended		9 Months Ended			12 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2019	Sep. 30, 2016
Debt Instrument [Line Items]
Face value							$ 30,000,000
Maximum borrowing capacity			$ 30,000,000				$ 50,000,000
EBITDA calculation expense threshold, acquisition expenses permissible			6,000,000
EBITDA calculation expense threshold, nonrecurring expenses			2,000,000
Cash and cash equivalents minimum balance	$ 25,000,000	$ 25,000,000	30,000,000
EBITDA target				$ 30,000,000	$ 25,000,000
Amount outstanding			$ 0
LIBOR Rate
Debt Instrument [Line Items]
Unused capacity, commitment fee percentage			0.25%
Total Leverage Ratio Less Than 1%
Debt Instrument [Line Items]
Unused capacity, commitment fee percentage			1.50%
Total Leverage Ratio Greater Or Equal 1%
Debt Instrument [Line Items]
Unused capacity, commitment fee percentage			2.50%
Scenario, Forecast
Debt Instrument [Line Items]
EBITDA target						$ 35,000,000

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Rental expense	$ 0.9	$ 0.6	$ 2.2	$ 2

Stockholders' Equity - Share-ba

Stockholders' Equity - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 13,818	$ 10,091	$ 37,503	$ 27,468
Cost of revenues
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	106	73	303	228
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	4,528	3,706	12,190	10,334
Sales and marketing
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,675	1,261	4,994	3,588
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 7,509	$ 5,051	$ 20,016	$ 13,318

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized share-based compensation		$ 0	$ 0
RSUs and PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs related to restricted stock units	$ 74,800,000	$ 74,800,000
Weighted average vesting period for recognition of compensation expense		1 year 7 months 2 days
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares repurchased (in shares)	983,284
Share price (in dollars per share)	$ 20.34	$ 20.34

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Restricted Stock Unit Activity (Details) - RSUs and PSUs	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Number of RSUs and PSUs Outstanding
Number of RSUs and PSUs Outstanding, Beginning (shares) | shares	14,335,115
Number of RSUs and PSUs, Granted (shares) | shares	3,452,774
Number of RSUs and PSUs, Released (shares) | shares	(5,249,303)
Number of RSUs and PSUs, Canceled (shares) | shares	(1,521,060)
Number of RSUs and PSUs Outstanding, Ending (shares) | shares	11,017,526
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance (in dollars per share) | $ / shares	$ 6.78
Weighted Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	21.35
Weighted Average Grant Date Fair Value, Released (in dollars per share) | $ / shares	6.48
Weighted Average Grant Date Fair Value, Canceled (in dollars per share) | $ / shares	6.95
Weighted Average Grant Date Fair Value, Ending balance (in dollars per share) | $ / shares	$ 11.47

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 713	$ 598	$ 1,682	$ 1,961

Restructuring Charges - Narrati

Restructuring Charges - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)position	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 17	$ 64	$ 252	$ 1,023	$ 1,047
Restructuring reserve	243		243		265	$ 306
Restructuring reserve, current	100		100
Restructuring reserve, noncurrent	100		$ 100
2017 Restructuring Plan | Workforce Reduction Costs
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | position			50
Restructuring charges			$ 82		941
Restructuring reserve	30		30		44	0
2017 Restructuring Plan | Lease Termination and Other Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			13		148
Restructuring reserve	0		0		0	0
2015 Restructuring Plan | Lease Termination and Other Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			157		(42)
Restructuring reserve	$ 213		$ 213		$ 221	$ 306

Restructuring Charges - Restruc

Restructuring Charges - Restructuring Reserve (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Beginning balance			$ 265	$ 306	$ 306
Restructuring charges	$ 17	$ 64	252	1,023	1,047
Cash payments			(256)		(1,068)
Write-offs			(18)		(20)
Ending balance	243		243		265
2017 Restructuring Plan | Workforce Reduction Costs
Restructuring Reserve [Roll Forward]
Beginning balance			44	0	0
Restructuring charges			82		941
Cash payments			(96)		(897)
Write-offs			0		0
Ending balance	30		30		44
2017 Restructuring Plan | Lease Termination and Other Costs
Restructuring Reserve [Roll Forward]
Beginning balance			0	0	0
Restructuring charges			13		148
Cash payments			(13)		(128)
Write-offs			0		(20)
Ending balance	0		0		0
2015 Restructuring Plan | Lease Termination and Other Costs
Restructuring Reserve [Roll Forward]
Beginning balance			221	$ 306	306
Restructuring charges			157		(42)
Cash payments			(147)		(43)
Write-offs			(18)		0
Ending balance	$ 213		$ 213		$ 221

Related-Party Transactions (Det

Related-Party Transactions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)board_member	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Adobe Systems | Chief Executive Officer
Related Party Transaction [Line Items]
Purchases from related party	$ 600,000	$ 800,000	$ 2,800,000	$ 2,600,000
Revenue from related parties	0	0	100,000	0
Due to related parties	200,000		200,000		$ 200,000
Receivables from related party	500,000		500,000		0
Cengage | Chief Executive Officer
Related Party Transaction [Line Items]
Revenue from related parties	1,200,000	1,200,000	3,200,000	1,800,000
Due to related parties	2,000,000		2,000,000		100,000
Receivables from related party					$ 300,000
Cengage | Board Of Directors Member
Related Party Transaction [Line Items]
Purchases from related party	3,800,000	4,700,000	$ 10,300,000	9,500,000
Number of board members appointed to Board of Directors of related party | board_member			1
Receivables from related party	0		$ 0
PayPal | Board Of Directors Member
Related Party Transaction [Line Items]
Number of board members appointed to Board of Directors of related party | board_member			1
Expenses from transactions with related party	400,000	$ 300,000	$ 1,000,000	$ 800,000
Synack, Inc. | Board Of Directors Member
Related Party Transaction [Line Items]
Purchases from related party	$ 100,000

Subsequent Event (Details)

Subsequent Event (Details) $ in Millions	Oct. 29, 2018USD ($)
Subsequent Event
Subsequent Event [Line Items]
Cost method investment	$ 10