Summary of Significant Accounting Policies (Components of Self-Insurance Reserves) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Policy Text Block [Abstract]
Self-insurance reserves (undiscounted)	$ 157,538	$ 147,664
Self-insurance reserves (discounted)	$ 146,718	$ 137,970

The undiscounted portion of self insurance reserves as of the balance sheet date.

No definition available.

Name:	orly_SelfInsuranceReservesUndiscounted
Namespace Prefix:	orly_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant