Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2011	Feb. 20, 2012	Jun. 30, 2011
Document and Entity Information
Document type	10-K
Amendment flag	false
Document period end date	Dec. 31, 2011
Document fiscal year focus	2011
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		127,315,291	135,955,214
Entity public float		$ 10,764,507,854	$ 8,906,426,069