Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenue from Contract with Customer [Abstract]
Number of reportable segments | segment									3
Guarantee period									90 days
Disaggregation of Revenue [Line Items]
Service revenues	$ 1,537,385	$ 1,552,132	$ 1,516,385	$ 1,468,530	$ 1,481,658	$ 1,466,226	$ 1,457,054	$ 1,395,333	$ 6,074,432	$ 5,800,271	$ 5,266,789
Accountemps
Disaggregation of Revenue [Line Items]
Service revenues									1,946,404	1,915,054	1,765,666
OfficeTeam
Disaggregation of Revenue [Line Items]
Service revenues									1,037,341	1,063,238	984,873
Robert Half Technology
Disaggregation of Revenue [Line Items]
Service revenues									722,535	682,889	629,278
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Service revenues									705,845	669,385	631,225
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Service revenues									4,412,125	4,330,566	4,011,042
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Service revenues									533,432	511,989	439,214
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Service revenues									$ 1,128,875	$ 957,716	$ 816,533