Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment			3
Guarantee period			90 days
Service revenues	$ 1,108,326	$ 1,516,385	$ 2,615,017	$ 2,984,915
Accountemps
Disaggregation of Revenue [Line Items]
Service revenues	322,596	486,992	803,037	970,465
OfficeTeam
Disaggregation of Revenue [Line Items]
Service revenues	132,730	261,034	371,766	513,069
Robert Half Technology
Disaggregation of Revenue [Line Items]
Service revenues	151,542	179,375	334,965	351,303
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Service revenues	146,518	175,311	335,738	352,502
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Service revenues	753,386	1,102,712	1,845,506	2,187,339
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Service revenues	71,030	140,894	191,519	272,456
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Service revenues	$ 283,910	$ 272,779	$ 577,992	$ 525,120