Disaggregation of Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 1,579,922	$ 1,397,700	$ 1,347,387
Flex revenue
Disaggregation of Revenue [Line Items]
Revenue	1,530,157	1,364,097	1,299,687
Direct Hire revenue
Disaggregation of Revenue [Line Items]
Revenue	49,765	33,603	47,700
Technology
Disaggregation of Revenue [Line Items]
Revenue	1,273,941	1,049,628	1,057,859
Technology | Flex revenue
Disaggregation of Revenue [Line Items]
Revenue	1,247,560	1,032,901	1,037,380
Technology | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Revenue	26,381	16,727	20,479
FA
Disaggregation of Revenue [Line Items]
Revenue	305,981	348,072	289,528
FA | Flex revenue
Disaggregation of Revenue [Line Items]
Revenue	282,597	331,196	262,307
FA | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 23,384	$ 16,876	$ 27,221