Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2012	Feb. 25, 2013	Jun. 30, 2012
Document and Entity Information
Document type	10-K
Amendment flag	false
Document period end date	Dec. 31, 2012
Document fiscal year focus	2012
Current fiscal year end date	--12-31
Document fiscal period focus	FY
Entity registrant name	O REILLY AUTOMOTIVE INC
Trading symbol	orly
Entity central index key	0000898173
Entity well-known seasoned issuer	Yes
Entity voluntary filers	No
Entity current reporting status	Yes
Entity filer category	Large Accelerated Filer
Entity common stock, shares outstanding		111,304,878	122,014,308
Entity public float		$ 11,280,749,385	$ 10,221,138,581