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Business Acquisitions and Dispositions - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2016 USD ($) Dealerships Franchise Business | Dec. 31, 2015 USD ($) Dealerships Franchise | Dec. 31, 2014 USD ($) Dealerships Franchise
Business Acquisition [Line Items] |  |  |
Number of businesses acquired |  | 0 |
Business acquisition, consideration amount | $ |  |  | $ 50.9
Number of franchises disposed | Dealerships | 0 | 4 | 9
Cash generated from disposition | $ |  | $ 8.0 | $ 74.8
Number of franchises classified as held for sale | 0 |  |
Franchised Dealerships [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of businesses opened | Business | 2 |  |
Echo Park [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of businesses opened | Business | 2 |  |
Stand-alone Used Vehicle Dealership Business and Real Estate [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of businesses acquired | Business | 3 |  |
Business acquisition, consideration amount | $ | $ 15.9 |  |
Luxury Franchise [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of businesses acquired |  |  | 2
Mid-line Import Franchise [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of businesses acquired |  |  | 1
Domestic Franchise [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Number of businesses acquired |  |  | 1

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- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477 + Details
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