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Description of Business and Summary of Significant Accounting Policies (Goodwill and Other Intangible Assets) (Details) - USD ($)	4 Months Ended	12 Months Ended
	Apr. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill and Intangible Assets [Line Items]
Franchise agreements, minimal contractual terms (in years)		1 year
Franchise rights impairment		$ 0	$ 15,400,000	$ 0
Goodwill [Member]
Goodwill and Intangible Assets [Line Items]
Date of annual goodwill and indefinite lived intangible assets impairment test		April 30	April 30
Franchise Rights [Member]
Goodwill and Intangible Assets [Line Items]
Date of annual goodwill and indefinite lived intangible assets impairment test		April 30	April 30
Maximum [Member]
Goodwill and Intangible Assets [Line Items]
Other intangibles, useful life		30 years
Minimum [Member]
Goodwill and Intangible Assets [Line Items]
Other intangibles, useful life		5 years
Nonrecurring [Member]
Goodwill and Intangible Assets [Line Items]
Goodwill impairment		$ 0	$ 0
Nonrecurring [Member] | Franchise Rights [Member]
Goodwill and Intangible Assets [Line Items]
Franchise rights impairment	$ 0	0
Nonrecurring [Member] | Franchise Rights [Member] | Volkswagen [Member]
Goodwill and Intangible Assets [Line Items]
Franchise rights impairment		$ 0	$ 15,400,000

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- Definition

The date of the annual goodwill and indefinite-lived franchise rights impairment test.

+ References

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- Definition

The minimum contractual term of the Company's various franchise agreements with vehicle manufacturers.

+ References

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Goodwill and Intangible Assets [Line Items]

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16373-109275

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