Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Disaggregation of Revenue [Line Items]
Guarantee Period			90 days
Number of reportable segments | segment			3
Net service revenues	$ 1,466,226	$ 1,324,709	$ 4,318,613	$ 3,920,507
Accountemps
Disaggregation of Revenue [Line Items]
Net service revenues	479,415	443,376	1,431,567	1,319,649
OfficeTeam
Disaggregation of Revenue [Line Items]
Net service revenues	265,235	246,207	794,749	726,755
Robert Half Technology
Disaggregation of Revenue [Line Items]
Net service revenues	176,552	157,038	508,060	472,309
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Net service revenues	162,564	158,187	503,652	471,997
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Net service revenues	1,083,766	1,004,808	3,238,028	2,990,710
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Net service revenues	129,667	111,333	386,105	327,619
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Net service revenues	$ 252,793	$ 208,568	$ 694,480	$ 602,178