Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 19, 2018	Jun. 30, 2017
Document and Entity Information
Document type	10-K
Amendment flag	false
Document period end date	Dec. 31, 2017
Document fiscal year focus	2017
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		83,670,900
Entity public float			$ 13,884,808,148