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Commitments and Contingencies - Additional Information (Details) - USD ($) | 6 Months Ended |
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Jun. 30, 2018 | Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract] |  |
Lease exit costs accrual | $ 7,554,000 | $ 6,478,000
Other Commitments [Line Items] |  |
Maximum exposure associated with general indemnifications | $ 17,000,000 | $ 5,000,000
General indemnifications minimum expiration period | 1 year |
General indemnifications maximum expiration period | 3 years |
Percentage of dealership that is accounted for under the equity method | 50.00% | 50.00%
Contingent liability reserve balance after reduction | $ 2,800,000 | $ 2,800,000
Acquired business, earnings targets, maximum term | 10 years |
Maximum aggregate earnout payment | $ 80,000,000 |
Earnout accrual | 23,300,000 |
Earnout accrual recorded in other accrued liabilities | 7,700,000 |
Earnout accrual recorded in other long-term liabilities | 15,600,000 |
Other accrued liabilities |  |
Other Commitments [Line Items] |  |
Amount reserved for pending proceedings | 4,700,000 | 3,000,000
Other long-term liabilities |  |
Other Commitments [Line Items] |  |
Amount reserved for pending proceedings | $ 200,000 | $ 200,000

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