Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total Revenue	$ 326,738		$ 317,441
Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	314,981		306,046
Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	11,757		11,395
Tech
Disaggregation of Revenue [Line Items]
Total Revenue	255,643		236,497
Tech | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	250,216	$ 250,216	231,496	$ 231,496
Tech | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	5,427	5,427	5,001	5,001
FA
Disaggregation of Revenue [Line Items]
Total Revenue	71,095		80,944
FA | Flex revenue
Disaggregation of Revenue [Line Items]
Total Revenue	64,765	64,765	74,550	74,550
FA | Direct Hire revenue
Disaggregation of Revenue [Line Items]
Total Revenue	$ 6,330	$ 6,330	$ 6,394	$ 6,394