Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment			3
Guarantee period			90 days
Net service revenues	$ 1,552,132	$ 1,466,226	$ 4,537,047	$ 4,318,613
Accountemps
Disaggregation of Revenue [Line Items]
Net service revenues	489,690	479,415	1,460,155	1,431,567
OfficeTeam
Disaggregation of Revenue [Line Items]
Net service revenues	265,941	265,235	779,010	794,749
Robert Half Technology
Disaggregation of Revenue [Line Items]
Net service revenues	185,268	176,552	536,571	508,060
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Net service revenues	177,562	162,564	530,064	503,652
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Net service revenues	1,118,461	1,083,766	3,305,800	3,238,028
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Net service revenues	134,582	129,667	407,038	386,105
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Net service revenues	$ 299,089	$ 252,793	$ 824,209	$ 694,480