Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment			3
Guarantee period			90 days
Net service revenues	$ 1,516,385	$ 1,457,054	$ 2,984,915	$ 2,852,387
Accountemps
Disaggregation of Revenue [Line Items]
Net service revenues	486,992	480,563	970,465	952,152
OfficeTeam
Disaggregation of Revenue [Line Items]
Net service revenues	261,034	268,362	513,069	529,514
Robert Half Technology
Disaggregation of Revenue [Line Items]
Net service revenues	179,375	171,446	351,303	331,508
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Net service revenues	175,311	167,603	352,502	341,088
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Net service revenues	1,102,712	1,087,974	2,187,339	2,154,262
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Net service revenues	140,894	135,038	272,456	256,438
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Net service revenues	$ 272,779	$ 234,042	$ 525,120	$ 441,687