Revenue Recognition - Schedule of Revenue Disaggregated by Line of Business (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment	3
Guarantee period	90 days
Service revenues	$ 1,506,691	$ 1,468,530
Accountemps
Disaggregation of Revenue [Line Items]
Service revenues	480,441	483,473
OfficeTeam
Disaggregation of Revenue [Line Items]
Service revenues	239,036	252,035
Robert Half Technology
Disaggregation of Revenue [Line Items]
Service revenues	183,423	171,928
Robert Half Management Resources
Disaggregation of Revenue [Line Items]
Service revenues	189,220	177,191
Temporary and consulting staffing
Disaggregation of Revenue [Line Items]
Service revenues	1,092,120	1,084,627
Permanent placement staffing
Disaggregation of Revenue [Line Items]
Service revenues	120,489	131,562
Risk consulting and internal audit services
Disaggregation of Revenue [Line Items]
Service revenues	$ 294,082	$ 252,341