Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 30, 2017
Document and Entity Information
Document type	10-Q
Amendment flag	false
Document period end date	Sep. 30, 2017
Document fiscal year focus	2017
Current fiscal year end date	--12-31
Document fiscal period focus	Q3
Entity registrant name	O REILLY AUTOMOTIVE INC
Entity central index key	0000898173
Entity filer category	Large Accelerated Filer
Entity common stock, shares outstanding		85,027,697