Stockholders' Equity - Number and Cost of Employee Stock Plan Repurchases (Details) - USD ($) shares in Thousands, $ in Thousands	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Repurchases related to employee stock plans (in shares)	154	311
Repurchases related to employee stock plans	$ 8,942	$ 15,058

Value of shares repurchased in connection with employee stock plans, whereby Company shares were tendered by employees for the payment of applicable withholding taxes and/or exercise price.

No definition available.

Name:	rhi_StockRepurchasedUnderEmployeeStockPlanDuringPeriodValue
Namespace Prefix:	rhi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration