Summary of Operations and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited condensed consolidated financial statements and accompanying notes have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, these financial statements do not include all information and footnotes required by GAAP for complete financial statements.
Unaudited Interim Financial Statements	The interim consolidated balance sheet as of September 30, 2017, consolidated statements of operations and comprehensive income for the three and nine months ended September 30, 2017 and 2016, and consolidated statement of cash flows for the nine months ended September 30, 2017 and 2016 are unaudited. The consolidated balance sheet as of December 31, 2016, included herein, was derived from the audited financial statements as of that date, but does not include all disclosures required by GAAP. These unaudited interim financial statements have been prepared on a basis consistent with the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary to state fairly the Company’s financial position as of September 30, 2017 and its consolidated results of operations, comprehensive income and cash flows for the three and nine months ended September 30, 2017 and 2016. The financial data and the other financial information disclosed in the notes to the financial statements related to these periods are also unaudited. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results to be expected for the fiscal year ending December 31, 2017 or for any other future annual or interim period. These financial statements should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto as of and for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K, which was filed with the SEC on February 27, 2017. The unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. During the second quarter of 2017, the Company recorded immaterial adjustments to its unaudited condensed consolidated financial statements to: (1) reduce revenue by approximately $0.6 million and (2) increase general and administrative expense by approximately $0.1 million, related to prior periods. During the third quarter of 2017, the Company recorded an immaterial adjustment to its unaudited condensed consolidated financial statements to increase revenue by approximately $0.9 million, related to prior periods. The Company has concluded that the impact of these adjustments is not material to the results of operations or financial position for the periods in which these adjustments were recorded nor any prior quarterly or annual period financial statements. Certain changes in presentation have been made to conform the prior period presentation to current period reporting.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements. Actual results could differ from those estimates. Such estimates include, but are not limited to, the determination of the allowance for doubtful accounts, the assessment of recoverability of property and equipment, the fair value of acquired goodwill and intangible assets, the grant-date fair value of non-cash equity-based compensation, the assessment of recoverability of deferred tax assets and the measurement of certain contingent non-income tax liabilities.
Restricted Cash	Restricted Cash The Company’s restricted cash relates to security deposits for its office leases. As of September 30, 2017 and December 31, 2016, the Company had restricted cash of approximately $2.6 million in other assets that related to the lease for its headquarters in New York City, which expires in 2029. The carrying value of restricted cash approximates fair value.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The Company’s accounts receivable consist of customer obligations due under normal trade terms, carried at their face value less an allowance for doubtful accounts, if required. The Company determines its allowance for doubtful accounts based on an evaluation of the aging of its accounts receivable and on a customer-by-customer basis where appropriate. The Company’s reserve analysis contemplates the Company’s historical loss rate on receivables, specific customer situations and the economic environments in which the Company operates. During the nine months ended September 30, 2017, bad debt expense, which increased the allowance for doubtful accounts, was $1.0 million, and write-offs and other adjustments, which decreased the allowance for doubtful accounts, were $2.5 million.
Deferred Rent	Deferred Rent The Company records rent expense on a straight-line basis over the term of the related lease. The difference between the rent expense recognized and the actual payments made in accordance with the lease agreement is recognized as a deferred rent liability on the Company’s balance sheet.
Chargeback and Sales Refund Allowance	Chargeback and Sales Refund Allowance The majority of the Company’s customers purchase products by making an electronic payment with a credit card at the time of a transaction. The Company establishes a chargeback allowance and sales refund reserve allowance based on factors surrounding historical credit card chargeback trends, historical sales refund trends and other information.
Recently Adopted and Issued Accounting Standard Updates	Recently Adopted Accounting Standard Updates In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employees Share-Based Payment Accounting (“ASU 2016-09”). This ASU changes how companies account for certain aspects of share-based payment awards to employees, including the requirement for all income tax effects related to settlements of share-based payment awards be reported in earnings as an increase or decrease to income tax expense, providing the Company an accounting policy election to either recognize forfeitures as they occur or record an estimate, and requires that all income tax-related cash flows resulting from share-based payments be reported as operating activities in the statement of cash flows. The Company adopted ASU 2016-09 on January 1, 2017. All income tax effects related to settlements of share-based payment awards will be reported as an increase or decrease to the provision for income taxes. In addition, starting January 1, 2017, the Company will account for forfeitures as they occur and, as of January 1, 2017, recognized a $0.7 million reduction to retained earnings as the cumulative effect of the change in accounting principle. The Company adopted the cash flow presentation component of ASU 2016-09 retrospectively, and accordingly, decreased cash flows from operating activities by $0.6 million and increased cash flows from financing activities by $0.6 million for the nine months ended September 30, 2016. Recently Issued Accounting Standard Updates In November 2016, the FASB issued ASU 2016-18, Statements of Cash Flows (Topic 230): Restricted Cash, which requires entities to present restricted cash with cash and cash equivalents on the statement of cash flows when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. ASU 2016-18 is effective for interim and annual periods beginning after December 15, 2017, with early adoption permitted. The Company is evaluating the impact of adopting this new accounting standard on its financial statements. The balance of the Company’s restricted cash was $2.6 million as of September 30, 2017. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses of Financial Instruments. ASU 2016-13 replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses. The ASU is intended to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. Adoption of this guidance is required, prospectively, for annual periods beginning after December 15, 2019, with early adoption permitted for annual periods beginning after December 15, 2018. The Company is evaluating the impact of adopting this new accounting standard on its financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 requires that the rights and obligations created by leases with a duration greater than 12 months be recorded as assets and liabilities on the balance sheet of the lessee. The guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018 and can be applied using a modified retrospective approach for all leases entered into before the effective date. Early adoption is permitted. The Company is evaluating the impact of adopting this new accounting standard on its financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). ASU 2014-09, and its related amendments, provides a unified model to determine when and how revenue is recognized and requires certain additional disclosures around the nature, amount, timing, and uncertainty of revenue and cash flows arising from customers. The core principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 will be effective for the fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted. This new guidance may be applied retrospectively to each prior period (full retrospective) or retrospectively with the cumulative effect recognized as of the date of initial application (modified retrospective). The Company expects to adopt this guidance in the first quarter of fiscal 2018 and apply the modified retrospective approach. The Company is evaluating the impact of adopting this new accounting standard on its financial statements. Management is progressing with its implementation plan and is considering relevant guidance and industry interpretations as it concludes on its performance obligations, variable consideration, and timing of revenue recognition.