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Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Increase in fair value of marketable securities	$ 3,600	$ 1,900
Non-financial assets and liabilities measured at fair value on a nonrecurring basis	$ 0	$ 0

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- Definition

Represents the aggregate of the non-financial assets and/or liabilities reported on the balance sheet at period end measured at fair value on a nonrecurring basis. Non-financial assets and liabilities may include assets acquired in a business combination or property and equipment that are determined to be impaired.

+ References

No definition available.

+ Details

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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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Definition

Amount of increase (decrease) in the fair value of equity or debt securities classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3444-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration