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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016
Significant Accounting Policies [Line Items] |  |  |  |  |
Effective tax rate from continuing operations | 39.30% | 39.60% | 39.80% | 39.30% |
Income tax benefit | $ (7,956) | $ (15,113) | $ (8,128) | $ (24,283) |
ASU 2016-09 [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax benefit | $ 200 |  | $ 500 |  |
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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