Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment			3
Net service revenues	$ 1,457,054	$ 1,308,428	$ 2,852,387	$ 2,595,798
Accountemps
Disaggregation of Revenue [Line Items]
Net service revenues	480,563	439,734	952,152	876,273
OfficeTeam
Disaggregation of Revenue [Line Items]
Net service revenues	268,362	244,369	529,514	480,548
Robert Half Technology
Disaggregation of Revenue [Line Items]
Net service revenues	171,446	157,832	331,508	315,271
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Net service revenues	167,603	156,361	341,088	313,810
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Net service revenues	1,087,974	998,296	2,154,262	1,985,902
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Net service revenues	135,038	112,653	256,438	216,286
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Net service revenues	$ 234,042	$ 197,479	$ 441,687	$ 393,610