Inventories - Components of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
New vehicles	$ 856,967sah_InventoryNewVehicles	$ 924,818sah_InventoryNewVehicles
Used vehicles	246,713sah_InventoryUsedVehicles	214,015sah_InventoryUsedVehicles
Service loaners	115,741sah_InventoryServiceLoaners	112,520sah_InventoryServiceLoaners
Parts, accessories and other	60,606us-gaap_OtherInventoriesSpareParts	60,349us-gaap_OtherInventoriesSpareParts
Net inventories	$ 1,280,027us-gaap_InventoryNet	$ 1,311,702us-gaap_InventoryNet

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6386567&loc=d3e3927-108312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant