Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment			3
Guarantee period			90 days
Service revenues	$ 1,580,581	$ 1,108,326	$ 2,978,961	$ 2,615,017
Elimination of Intersegment Revenues
Disaggregation of Revenue [Line Items]
Service revenues	(143,036)	(41,514)	(246,840)	(87,786)
Accountemps
Disaggregation of Revenue [Line Items]
Service revenues	453,342	331,542	870,448	821,426
OfficeTeam
Disaggregation of Revenue [Line Items]
Service revenues	263,192	136,299	483,665	376,278
Robert Half Technology
Disaggregation of Revenue [Line Items]
Service revenues	194,233	162,028	366,406	358,680
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Service revenues	210,550	165,031	393,878	376,908
Temporary and consultant staffing
Disaggregation of Revenue [Line Items]
Service revenues	978,281	753,386	1,867,557	1,845,506
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Service revenues	143,640	71,030	255,344	191,519
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Service revenues	$ 458,660	$ 283,910	$ 856,060	$ 577,992