Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States (U.S. GAAP) requires management to make estimates, judgments, and assumptions that affect the reported amounts of assets and liabilities; the disclosure of contingent liabilities at the date of the financial statements; and the reported amounts of revenues and expenses during the reporting periods. Significant estimates, assumptions, and judgments are used for, but not limited to: revenue recognition, recoverability of accounts receivable, restructuring charges (credits), share-based compensation expense including estimated forfeitures, accounting for income taxes, useful lives assigned to long-lived assets for depreciation and amortization, impairment of goodwill and long-lived assets, the valuation of acquired intangible assets, and the valuation of our convertible senior notes. 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.
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of Chegg and our wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in accordance with U.S. GAAP.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash We consider all highly liquid investments with an original maturity date of three months or less from the date of purchase to be cash equivalents. Our cash and cash equivalents consist of cash, money market accounts, and commercial paper at financial institutions, are stated at cost, which approximates fair value. We classify certain restricted cash balances within other current assets and other assets on the accompanying consolidated balance sheets based upon the term of the remaining restrictions.
Investments	Investments We hold investments in commercial paper, corporate securities and U.S. treasury securities. We classify our marketable securities as available-for-sale investments that are either short or long-term based on the nature of each security based on the contractual maturity of the investment when purchased. Our available-for-sale investments are carried at estimated fair value with any unrealized gains and losses, net of taxes, included in accumulated other comprehensive loss in stockholders’ equity. Unrealized losses are charged against other income (expense), net when a decline in fair value is determined to be other-than-temporary. We did not record any such impairment charges in the periods presented. We determined realized gains or losses on the sale of marketable securities on a specific identification method, and recorded such gains or losses as other income (expense), net.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable Accounts receivable are recorded at the invoiced amount and are non-interest bearing. We generally grant uncollateralized credit terms to our customers, which include textbook wholesalers, and marketing services customers, and maintain an allowance for doubtful accounts to account for potentially uncollectible receivables. Allowance for Doubtful Accounts We assess the creditworthiness of our customers based on multiple sources of information, and analyze such factors as our historical bad debt experience, industry and geographic concentrations of credit risk, economic trends, and customer payment history. This assessment requires significant judgment. Because of this assessment, we maintain an allowance for doubtful accounts for estimated losses resulting from the inability of certain customers to make all of their required payments. In making this estimate, we analyze historical payment performance and current economic trends when evaluating the adequacy of the allowance for doubtful accounts. Accounts receivable are written off as a decrease to the allowance for doubtful accounts when all collection efforts have been exhausted and an account is deemed uncollectible.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents, restricted cash, and marketable securities invested in highly liquid instruments in accordance with our investment policy. We place the majority of our cash and cash equivalents and restricted cash with a financial institution in the United States that we believe to be of high credit quality, and accordingly minimal credit risk exists with respect to these instruments. Certain of our cash balances held with a financial institution are in excess of Federal Deposit Insurance Corporation limits. Our investment portfolio consists of investment-grade marketable securities diversified among security types, industries and issuers. Our investments were held and managed by a recognized financial institution that followed our investment policy with the main objective of preserving capital and maintaining liquidity. C
Property and Equipment	Depreciation and content amortization expense are generally classified within the corresponding cost of revenues and operating expenses categories in our consolidated statements of operations. The cost of maintenance and repairs is expensed as incurred. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from their respective accounts, and any gain or loss on such sale or disposal is reflected in loss from operations Property and Equipment Property and equipment are recorded at cost less accumulated depreciation and content amortization. Depreciation and content amortization are computed using the straight-line method over the following estimated useful lives of the assets:
Business Combinations	Business Combinations We allocate the fair value of purchase consideration to the tangible assets acquired, liabilities assumed and intangible assets acquired through a business combination based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets acquired and liabilities assumed is recorded as goodwill. Such valuations require management to make significant estimates and assumptions, especially with respect to intangible assets. Significant estimates in valuing certain intangible assets include, but are not limited to, future expected cash flows from acquired users, acquired technology, and trade names from a market participant perspective, useful lives and discount rates. Management’s estimates of fair value are based upon assumptions believed to be reasonable, but which are inherently uncertain and unpredictable and, as a result, actual results may differ from estimates. During the measurement period, which is not to exceed one year from the acquisition date, we may record adjustments to the assets acquired and liabilities assumed, with the corresponding offset to goodwill. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings.
Goodwill and Indefinite-Lived Intangible Asset	Goodwill and Indefinite-Lived Intangible Asset Goodwill represents the excess of the fair value of purchase consideration paid over the estimated fair value of assets acquired and liabilities assumed in a business combination. Our indefinite-lived intangible asset represents the internships.com trade name. Goodwill and our indefinite-lived intangible asset are not amortized but rather tested for impairment at least annually on October 1, or more frequently if certain events or indicators of impairment occur between annual impairment tests. We first assess qualitative factors to determine whether it is necessary to perform the quantitative impairment test. In our qualitative assessment, we consider factors including economic conditions, industry and market conditions and developments, overall financial performance and other relevant entity-specific events in determining whether it is more likely than not that the fair value of our reporting unit is less than the carrying amount. We completed our annual impairment test on October 1 of 2018 and 2017, each of which did not result in any impairment as our qualitative assessment did not indicate that it is more likely than not that the fair value of our reporting unit is less than the carrying amount. As of December 31, 2018 and 2017, we had goodwill of $149.5 million and $125.3 million, respectively, and an indefinite lived intangible asset related to the internships.com trade name of $3.6 million.
Acquired Intangible Assets, and Other Long-Lived Assets	Acquired Intangible Assets and Other Long-Lived Assets Acquired intangible assets with finite useful lives, which include developed technology, customer lists, trade names, non-compete agreements, and master service agreements, are amortized over their estimated useful lives. We assess the impairment of acquired intangible assets and other long-lived assets when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable.
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 Chegg Study, Chegg Writing, Chegg Tutors, and Chegg Math Solver. Chegg Services are offered to students primarily through weekly or monthly subscriptions, and we recognize revenues ratably over the respective subscription period. Revenues from our Required Materials product line includes a revenue share on the rental and sale of print textbooks, as well as revenues from eTextbooks. The revenue share on the rental and sale of print textbooks is recognized immediately when a book ships to the student. Revenues from the rental of eTextbooks is recognized ratably over the contractual period, generally two to five months. Revenues from the sale of eTextbooks is recognized immediately when the eTextbook sale occurs. 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. Some of our customer arrangements 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 multiple 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. Our agreements with print textbook partners may include 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. 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. 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. In relation to print textbook rental and sale agreements with our partners, we recognize revenues on a net basis based on our role in the transaction as an agent as we have concluded that we do not control the use of the print textbooks, and therefore record only 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. Contract assets are contained within other current assets on our 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 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 consolidated balance sheets. Deferred revenue primarily consists of advanced payments from students related to rental and subscription performance obligations that have not been satisfied and estimated variable consideration. 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.
Cost of Revenues	Cost of Revenues Our cost of revenues consists primarily of expenses associated with the delivery and distribution of our products and services. Certain cost of revenues, including textbook depreciation expense, the cost of textbooks sold, write-offs and allowances related to the print textbook library, have decreased during 2016 and 2017 as we have completely transitioned the shipping and fulfillment activities related to the rental and sale of print textbooks to Ingram. Cost of revenues primarily consists of publisher content fees for eTextbooks, content amortization expense related to content that we develop or license, including publisher agreements for which we pay one-time license fees for published content, payment processing costs, the payments made to tutors through our Chegg Tutors service, personnel costs and other direct costs related to providing content or services. In addition, cost of revenues includes allocated information technology and facilities costs.
Research and Development Costs	Research and Development Costs Our research and development expenses consist of salaries, benefits and share-based compensation expense for employees in our product and web design, engineering and technical teams who are responsible for maintaining our website, developing new products and improving existing products. Research and development costs also include amortization of acquired intangible assets, depreciation expense, technology costs to support our research and development, outside services, and allocated information technology and facilities expenses. We expense substantially all of our research and development expenses as they are incurred.
Advertising Costs	Advertising Costs Advertising costs are expensed as incurred and consist primarily of online advertising and marketing promotional expenditures.
Share-based Compensation	Share-based Compensation Share-based compensation expense for stock options, restricted stock units (RSUs), performance-based restricted stock units (PSUs), and employee stock purchase plan (ESPP) are accounted for under the fair value method, which requires us to measure the cost of share-based compensation awards based on the grant-date fair value of the award. Share-based compensation expense for stock options and our ESPP is estimated at the date of grant using the Black-Scholes-Merton option pricing model while expense for RSUs and PSUs is measured based on the closing fair market value of the Company’s common stock on the date of grant. We recognize share-based compensation expense over the requisite service period, which is generally the vesting period, on a straight-line basis for RSUs and on a graded basis for PSUs, contingent on the achievement of performance conditions. These amounts are reduced by estimated forfeitures, which are estimated at the time of the grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
Income Taxes	Income Taxes We account for income taxes under an asset and liability method whereby deferred tax asset and liability account balances are determined based on differences between the financial reporting and the tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are established, when necessary, to reduce deferred tax assets to an amount that is more likely than not to be realized. We recognize the benefit from a tax position only if it is more likely than not that the position would be sustained upon audit based solely on the technical merits of the tax position. Our policy is to include interest and penalties related to unrecognized tax benefits as a component of income tax expense.
Restructuring Charges	Restructuring Charges Restructuring charges are primarily comprised of severance costs, contract and program termination costs, asset impairments and costs of facility consolidation and closure. Restructuring charges are recorded upon approval of a formal management plan and are included in the operating results of the period in which such plan is approved and the expense becomes estimable. To estimate restructuring charges, management utilizes assumptions of the number of employees that would be involuntarily terminated and of future costs to operate and eventually vacate duplicate facilities. Severance and other employee separation costs are accrued when it is probable that benefits will be paid and the amount is reasonably estimable. The rates used in determining severance accruals are based on our policies and practices and negotiated settlements. Restructuring charges for employee workforce reductions are recorded upon employee notification for employees whose required continuing service period is 60 days or less and ratably over the employee’s continuing service period for employees whose required continuing service period is greater than 60 days.
Strategic Investments	Strategic Investments We have entered into strategic investments that are accounted for under the cost method and included in other assets on our consolidated balance sheets. Our investments are periodically reviewed for other-than-temporary declines in fair value based on the specific identification method and write down the value of our investment when an other-than-temporary decline has occurred. Any fair value estimates are made based on consideration of the current cash position, recent operational performance, and forecasts of the investees.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential shares of common stock, including stock options, warrants, RSUs, PSUs, and shares related to convertible senior notes, to the extent dilutive. Basic and diluted net loss per share was the same for each period presented as the inclusion of all potential common shares outstanding would have been anti-dilutive.
Foreign Currency Translations	Foreign Currency Translation The functional currency of our foreign subsidiaries is the local currency. Adjustments resulting from the translation of foreign currencies into U.S. dollars for balance sheet amounts are based on the exchange rates as of the consolidated balance sheet date. Non-monetary balance sheet items denominated in a currency other than the applicable functional currency are translated using the historical rate. Revenues and expenses are translated at average exchange rates during the period. Foreign currency translation gains or losses are included in accumulated other comprehensive loss as a component of stockholders’ equity on the consolidated balance sheets. Gains or losses resulting from foreign currency transactions, which are denominated in currencies other than the entity’s functional currency, are included in other income (expense), net in the consolidated statements of operations and were not material during the years ended December 31, 2018, 2017 or 2016.
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 will 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 will elect this transition method of adoption. We will adopt the guidance on January 1, 2019. We expect to initially record a right of use asset of approximately $17 million and a lease liability of approximately $21 million with an immaterial cumulative-effect adjustment to the opening balance of accumulated deficit. We do not expect our adoption of ASU 2016-02 to have a material impact to our consolidated statements of operations. These are preliminary estimates that are subject to change as we finalize our adoption. 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 have applied 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 and have applied 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 consolidated statements of cash flows and include such amounts when reconciling beginning-of-period and end-of-period total amounts shown on the 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 consolidated statement of cash flows to include restricted cash with the change in restricted cash included within the other assets line on our 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 consolidated statement of operations. We have two strategic investments recorded in other assets on our consolidated balance sheets that fall 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 investments as there are not readily determinable fair values, which we are applying to our strategic investments starting with our adoption date of January 1, 2018. These investments are measured at cost, less any impairment, plus or minus adjustments resulting from observable price changes in orderly transactions for identical or similar investments of the same issuers, with any changes in the value of the investments recorded within the 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 3 for more information.