Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment	3
Guarantee period	90 days
Net service revenues	$ 1,468,530	$ 1,395,333
Accountemps
Disaggregation of Revenue [Line Items]
Net service revenues	483,473	471,589
OfficeTeam
Disaggregation of Revenue [Line Items]
Net service revenues	252,035	261,152
Robert Half Technology
Disaggregation of Revenue [Line Items]
Net service revenues	171,928	160,062
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Net service revenues	177,191	173,485
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Net service revenues	1,084,627	1,066,288
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Net service revenues	131,562	121,400
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Net service revenues	$ 252,341	$ 207,645