Business Segments - Reconciliation of Revenue and Operating Income by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Service revenues	$ 1,814,834	$ 1,398,380
Segment income	227,651	150,637
Amortization of intangible assets	417	576
Interest income, net	(166)	(45)
Income before income taxes	227,400	150,106
Contract talent solutions
Segment Reporting Information [Line Items]
Service revenues	1,155,723	889,275
Segment income	133,246	75,535
Permanent placement talent solutions
Segment Reporting Information [Line Items]
Service revenues	186,782	111,703
Segment income	37,328	17,780
Protiviti
Segment Reporting Information [Line Items]
Service revenues	472,329	397,402
Segment income	$ 57,077	$ 57,322