Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment	3
Guarantee period	90 days
Service revenues	$ 1,398,380	$ 1,506,691
Elimination of intersegment revenues
Disaggregation of Revenue [Line Items]
Service revenues	(103,818)	(46,273)
Accountemps
Disaggregation of Revenue [Line Items]
Service revenues	417,116	489,884
OfficeTeam
Disaggregation of Revenue [Line Items]
Service revenues	220,467	239,979
Robert Half Technology
Disaggregation of Revenue [Line Items]
Service revenues	172,239	196,652
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Service revenues	183,271	211,878
Temporary and consultant staffing
Disaggregation of Revenue [Line Items]
Service revenues	889,275	1,092,120
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Service revenues	111,703	120,489
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Service revenues	$ 397,402	$ 294,082