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           Business Acquisitions and Dispositions - Results Associated with Dealerships Classified as Discontinued Operations (Detail) (USD $) 
        In Thousands, unless otherwise specified  | 
        3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| 
           Sep. 30, 2014 
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           Sep. 30, 2013 
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           Sep. 30, 2014 
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           Sep. 30, 2013 
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| Business Combinations [Abstract] | ||||
| Income (loss) from operations | $ (900) | $ (1,389) | $ (1,670) | $ (22) | 
| Gain (loss) on disposal | 148 | (57) | 201 | (435) | 
| Lease exit accrual adjustments and charges | 1,006 | (611) | 631 | (1,977) | 
| Pre-tax income (loss) | 254 | (2,057) | (838) | (2,434) | 
| Total revenues | $ 0 | $ 0 | $ 0 | $ 0 | 
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- Definition 
          Discontinued operation lease exit accrual adjustments and charges. No definition available. 
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- Details 
          
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- Definition 
          Amount of gain (loss), before tax expense or benefit and not previously recognized, resulting from the sale of a business component. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition 
          Amount of operating income or loss attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Amount of sales or other form of revenues attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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