Summary of Significant Accounting Policies (Components of Self-Insurance Reserves) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Self-insurance reserves (undiscounted)	$ 168,397	$ 157,538
Self-insurance reserves (discounted)	$ 156,585	$ 146,718

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