Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document and Entity Information
Document type	10-Q
Amendment flag	false
Document period end date	Mar. 31, 2018
Document fiscal year focus	2018
Current fiscal year end date	--12-31
Document fiscal period focus	Q1
Entity registrant name	O REILLY AUTOMOTIVE INC
Entity central index key	0000898173
Entity filer category	Large Accelerated Filer
Entity common stock, shares outstanding		81,911,743