Document and Entity Information	9 Months Ended
	Sep. 30, 2018 shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	RHI
Entity Registrant Name	HALF ROBERT INTERNATIONAL INC /DE/
Entity Central Index Key	0000315213
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	121,475,032