Revenue Recognition - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total Revenue	$ 346,293	$ 333,992
Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	332,817	319,332
Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	11,395	11,505
Product revenue
Disaggregation of Revenue [Line Items]
Total Revenue	2,081	3,155
Tech
Disaggregation of Revenue [Line Items]
Total Revenue	236,497	222,045
Tech | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	231,496	216,886
Tech | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	5,001	5,159
Tech | Product revenue
Disaggregation of Revenue [Line Items]
Total Revenue	0	0
FA
Disaggregation of Revenue [Line Items]
Total Revenue	80,944	87,295
FA | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	74,550	80,949
FA | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	6,394	6,346
FA | Product revenue
Disaggregation of Revenue [Line Items]
Total Revenue	0	0
GS
Disaggregation of Revenue [Line Items]
Total Revenue	28,852	24,652
GS | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	26,771	21,497
GS | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	0	0
GS | Product revenue
Disaggregation of Revenue [Line Items]
Total Revenue	$ 2,081	$ 3,155