Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 29, 2018
Document and Entity Information
Document type	10-Q
Amendment flag	false
Document period end date	Sep. 30, 2018
Document fiscal year focus	2018
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 small business	false
Entity emerging growth company	false
Entity common stock, shares outstanding		80,104,348