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Summary of Significant Accounting Policies (Components of Self-Insurance Reserves) (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Policy Text Block [Abstract] |  |
Self-insurance reserves (undiscounted) | $ 147,664 | $ 138,687
Self-insurance reserves (discounted) | $ 137,970 | $ 129,437

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- Definition The discounted portion of self insurance reserves as of the balance sheet date. + References No definition available. + Details
Name: | orly_SelfInsuranceReservesDiscounted
Namespace Prefix: | orly_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The undiscounted portion of self insurance reserves as of the balance sheet date. + References No definition available. + Details
Name: | orly_SelfInsuranceReservesUndiscounted
Namespace Prefix: | orly_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_PolicyTextBlockAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration