Summary of Significant Accounting Policies (Components of Self-Insurance Reserves) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies
Self-insurance reserves (undiscounted)	$ 213,332	$ 168,397
Self-insurance reserves (discounted)	$ 202,454	$ 156,585

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