Description of Business and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Segment Information	Segment Information The Company operates in one reportable segment. All of the Company’s service revenues are generated from external clients. Less than 1% of revenue is generated outside of the United States of America (U.S.). Substantially all of the Company’s long-lived assets are located in the U.S.
Basis of Presentation	Basis of Presentation These unaudited condensed consolidated financial statements (Financial Statements) and accompanying notes have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) and applicable rules and regulations of the Securities and Exchange Commission (SEC) regarding interim financial reporting and, in the opinion of management, reflect all adjustments, consisting of normally recurring adjustments, necessary for fair presentation of the interim financial results of the Company. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. In addition, all intercompany accounts and transactions have been eliminated in consolidation. Therefore, these Financial Statements and notes should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2015. The accompanying unaudited condensed consolidated balance sheets present the current assets and current liabilities directly related to the processing of HR transactions as WSE-related assets and WSE-related liabilities, respectively. WSE-related assets consist of cash and investments restricted for current workers compensation claim payments, payroll funds collected, accounts receivable, unbilled service revenues, and refundable or prepaid amounts related to the Company-sponsored workers compensation and health plan programs. WSE-related liabilities consist of client prepayments, wages and payroll taxes accrued and payable, and liabilities related to the Company-sponsored workers compensation and health plan programs resulting from workers compensation case reserves, premium amounts due to providers for enrolled employees, and workers compensation and health reserves that are expected to be disbursed within the next 12 months. Certain prior period amounts in the Financial Statements have been reclassified to conform to the current presentation. The results of the nine months ended September 30, 2016 are not necessarily indicative of the results to be expected for the year ending December 31, 2016.
Use of Estimates	Seasonality and Insurance Variability The Company's business is affected by cyclicality in business activity and WSE behavior. Historically, the Company has experienced its highest monthly addition of WSEs, as well as its highest monthly levels of client attrition, in the month of January, primarily because clients that change their payroll service providers tend to do so at the beginning of a calendar year. In addition, the Company experiences higher levels of client attrition in connection with renewals of the health insurance TriNet sponsors for its WSEs, in the event that such renewals result in higher costs to its clients. The Company has also historically experienced higher insurance claim volumes in the second and third quarters of the year than in the first and fourth quarters, as WSEs typically access their health care providers more often in the second and third quarters, which has negatively impacted the Company's insurance costs in these quarters. The Company has also experienced variability on a quarterly basis in the amount of our health and workers compensation insurance costs due to the number and severity of insurance claims being unpredictable. These historical trends may change, and other seasonal trends and variability may develop which could make it more difficult for the Company to manage its business. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect certain reported amounts and disclosures. These estimates include, but are not limited to, allowances for accounts receivable, workers compensation-related reserve estimates, health plan reserve estimates, recoverability of goodwill and other intangible assets, income taxes, stock-based compensation and other contingent liabilities. Such estimates are based on historical experience and on various other assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-15—Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The new guidance is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. The amendment is effective for annual reporting periods, and interim periods within those years beginning after December 15, 2017. Early adoption is permitted, provided that all of the amendments are adopted in the same period. The guidance requires application using a retrospective transition method. The Company is currently in the process of evaluating the impact of the adoption of this standard on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, as part of the Simplification Initiative. The areas for simplification in this update involve several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. Some of the areas for simplification apply only to nonpublic entities. The amendment is effective for annual reporting periods, and interim periods within those years beginning after December 15, 2016. Early adoption is permitted. The Company is currently in the process of evaluating the impact of the adoption of this standard on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02—Leases. The amendment requires that lease arrangements longer than 12 months result in an entity recognizing an asset and liability. The amendment is effective for annual reporting periods, and interim periods within those years beginning after December 15, 2018. Early adoption is permitted. The Company is currently in the process of evaluating the impact of the adoption of this standard on its consolidated financial statements. In April 2015, the FASB issued ASU 2015-03—Simplifying the Presentation of Debt Issuance Costs, and, in August 2015, the FASB issued ASU 2015-15, Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements. These ASUs require debt issuance costs related to a recognized debt liability to be presented in the balance sheet as a direct deduction from the carrying amount of that debt, which is consistent with the presentation of debt discounts and premiums. The presentation and subsequent measurement of debt issuance costs associated with lines of credit, may be presented as an asset and amortized ratably over the term of the line of credit arrangement, regardless of whether there are outstanding borrowings on the arrangement. The recognition and measurement guidance for debt issuance costs are not affected by these ASUs. The Company adopted these ASUs as of March 31, 2016. The adoption of these ASUs resulted in a reclassification of unamortized debt issuance costs of $2.4 million from other current assets to current portion of notes payable and borrowings under capital leases and $3.4 million from other assets to notes payable and borrowings under capital leases, less current portion, as of December 31, 2015. Unamortized debt issuance costs related to the Company’s revolving credit facility will remain classified as an other asset in the accompanying consolidated balance sheets. The adoption of this guidance did not have any impact on the Company’s consolidated statements of operations, comprehensive income or cash flows. In May 2014, the FASB issued ASU 2014-09—Revenue from Contracts with Customers, which will replace most existing revenue recognition guidance under GAAP. The core principle of the guidance is that an entity 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. The standard provides a five-step analysis of transactions to determine when and how revenue is recognized. In July 2015, the FASB deferred the effective date to annual reporting periods, and interim periods within those years, beginning after December 15, 2017. Early adoption at the original effective date of December 15, 2016 is permitted. The amendments may be applied retrospectively or as a cumulative-effect adjustment as of the date of adoption. In March, April and May 2016, the FASB issued ASU 2016-08 Principal versus Agent Considerations (Reporting Revenue Gross versus Net), ASU 2016-10 Identifying Performance Obligations and Licensing and ASU 2016-12 Narrow-Scope Improvements and Practical Expedients, respectively, providing further clarification to be considered when implementing ASU 2014-09. The Company has not yet selected a method of adoption and is currently evaluating the effect that the amendments will have on the consolidated financial statements.