Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)
Revenue from Contract with Customer [Abstract]
Number of reportable segments | segment	3
Guarantee period	90 days
Disaggregation of Revenue [Line Items]
Service revenues	$ 1,814,834	$ 1,398,380
Elimination of Intersegment Revenues
Disaggregation of Revenue [Line Items]
Service revenues	(144,200)	(103,818)
Finance and accounting
Disaggregation of Revenue [Line Items]
Service revenues	801,690	600,387
Administrative and customer support
Disaggregation of Revenue [Line Items]
Service revenues	284,906	220,467
Technology
Disaggregation of Revenue [Line Items]
Service revenues	213,327	172,239
Total contract talent solutions
Disaggregation of Revenue [Line Items]
Service revenues	1,155,723	889,275
Permanent placement talent solutions
Disaggregation of Revenue [Line Items]
Service revenues	186,782	111,703
Protiviti
Disaggregation of Revenue [Line Items]
Service revenues	$ 472,329	$ 397,402