Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Revenue from Contract with Customer [Abstract]
Number of reportable segments | segment									3
Guarantee period									90 days
Disaggregation of Revenue [Line Items]
Net service revenues	$ 1,481,658	$ 1,466,226	$ 1,457,054	$ 1,395,333	$ 1,346,282	$ 1,324,709	$ 1,308,428	$ 1,287,370	$ 5,800,271	$ 5,266,789	$ 5,250,399
Accountemps
Disaggregation of Revenue [Line Items]
Net service revenues									1,915,054	1,765,666	1,786,276
OfficeTeam
Disaggregation of Revenue [Line Items]
Net service revenues									1,063,238	984,873	972,414
Robert Half Technology
Disaggregation of Revenue [Line Items]
Net service revenues									682,889	629,278	659,844
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Net service revenues									669,385	631,225	608,243
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Net service revenues									4,330,566	4,011,042	4,026,777
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Net service revenues									511,989	439,214	419,314
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Net service revenues									$ 957,716	$ 816,533	$ 804,308