Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total Revenue	$ 402,725	$ 365,424	$ 1,169,564	$ 1,043,652
Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	389,173	356,687	1,134,382	1,019,213
Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	13,552	8,737	35,182	24,439
Tech
Disaggregation of Revenue [Line Items]
Total Revenue	337,230	260,251	927,518	782,785
Tech | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	330,170	256,118	909,599	770,635
Tech | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	7,060	4,133	17,919	12,150
FA
Disaggregation of Revenue [Line Items]
Total Revenue	65,495	105,173	242,046	260,867
FA | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	59,003	100,569	224,783	248,578
FA | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	$ 6,492	$ 4,604	$ 17,263	$ 12,289