Business Segments - Reconciliation of Revenue and Operating Income by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Service revenues	$ 1,862,827	$ 1,580,581	$ 3,677,661	$ 2,978,961
Segment income	240,531	204,589	468,182	355,225
Amortization of intangible assets	416	576	833	1,152
Interest (income) expense, net	(718)	151	(884)	105
Income before income taxes	240,833	203,862	468,233	353,968
Contract talent solutions
Segment Reporting Information [Line Items]
Service revenues	1,165,693	978,281	2,321,416	1,867,557
Segment income	133,567	94,010	266,813	169,688
Permanent placement talent solutions
Segment Reporting Information [Line Items]
Service revenues	200,096	143,640	386,878	255,344
Segment income	36,751	30,599	74,079	48,234
Protiviti
Segment Reporting Information [Line Items]
Service revenues	497,038	458,660	969,367	856,060
Segment income	$ 70,213	$ 79,980	$ 127,290	$ 137,303