Fair Value Measurements (Notes)	3 Months Ended
Fair Value Measurements (Notes)	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Recurring Fair Value Measurements — The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable and accrued payroll and contract professional pay approximate their fair value based on their short-term nature. The carrying amount of long-term debt recorded in the Company’s condensed consolidated balance sheet at March 31, 2021 was $1.0 billion and approximated its fair value (see Note 4. Long-Term Debt), which was determined using quoted prices in active markets for identical liabilities (Level 1 inputs). The Company had investments, primarily mutual funds of $14.1 million and $14.4 million at March 31, 2021 and December 31, 2020, respectively, held in a rabbi trust restricted to fund the Company's deferred compensation plan, which are measured at fair value using the net asset value practical expedient. These assets were primarily included in other noncurrent assets in the accompanying condensed consolidated balance sheets. Certain acquisitions completed in 2020 contained provisions requiring that the Company pay contingent consideration in the event the acquired businesses achieved certain specified earnings results in 2021. The Company determined the fair value of the contingent consideration as of each acquisition date using a valuation model which included the evaluation of the expected performance of the acquired entity against the target performance metric and the application of an appropriate discount rate (Level 3 inputs). At the end of each reporting period, the fair value of the contingent consideration was remeasured and any changes were recorded as an adjustment to goodwill if the purchase accounting window was still open. Contingent consideration liabilities with fair values of $5.0 million at March 31, 2021 and December 31, 2020 were included in other current liabilities and other non-current liabilities in the accompanying condensed consolidated balance sheets, respectively. Nonrecurring Fair Value Measurements —Certain assets, such as goodwill and trademarks, are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances, such as, when there is evidence of impairment. There were no fair value adjustments for non-financial assets or liabilities during the three months ended March 31, 2021 and 2020.

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.