Stockholders' Equity - Number and Cost of Employee Stock Plan Repurchases (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Repurchases related to employee stock plans (in shares)	235	408	359
Repurchases related to employee stock plans	$ 13,674	$ 20,391	$ 15,170

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