Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment			3
Guarantee period			90 days
Service revenues	$ 1,189,897	$ 1,552,132	$ 3,804,914	$ 4,537,047
Elimination of intersegment revenues
Disaggregation of Revenue [Line Items]
Service revenues	(59,816)	(46,518)	(147,603)	(121,555)
Accountemps
Disaggregation of Revenue [Line Items]
Service revenues	351,598	501,905	1,173,024	1,486,571
OfficeTeam
Disaggregation of Revenue [Line Items]
Service revenues	173,685	267,023	549,963	781,607
Robert Half Technology
Disaggregation of Revenue [Line Items]
Service revenues	161,007	195,630	519,687	567,517
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Service revenues	154,917	200,421	531,826	591,660
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Service revenues	781,391	1,118,461	2,626,897	3,305,800
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Service revenues	87,203	134,582	278,722	407,038
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Service revenues	$ 321,303	$ 299,089	$ 899,295	$ 824,209