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Summary of Significant Accounting Policies - Additional Information (Detail) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2015 | Sep. 30, 2014 | Sep. 30, 2015 | Sep. 30, 2014 | Dec. 31, 2014
Significant Accounting Policies [Line Items] |  |  |  |  |
Effective tax rate from continuing operations | 40.00% | 38.00% | 39.50% | 38.70% |
Minimum [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Expected effective tax rate for continuing operations Range |  |  | 38.00% |  |
Maximum [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Expected effective tax rate for continuing operations Range |  |  | 40.00% |  |
Dealership [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Percentage of dealership that is accounted for under the equity method | 50.00% |  | 50.00% |  | 50.00%

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- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 + Details
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