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Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Jan. 01, 2018 | Dec. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Contract work in process |  |  | $ 4,700 |  |  |
Contract assets |  |  |  |  | $ 2,082 |
Percentage of dealership that is accounted for under the equity method | 50.00% |  | 50.00% |  |  | 50.00%
Effective tax rate from continuing operations | 32.40% | 41.70% | 31.10% | 41.00% |  |
Discrete charge for non-deductible executive compensation, transition costs | $ 800 |  | $ 800 |  |  |
Tax expense for uncertain tax positions |  |  | 200 |  |  |
Discrete charge for non-deductible disposition |  |  | 600 |  |  |
Discrete benefit related to vested or exercised stock compensation |  |  | 900 |  |  |
Discrete charge related to non-deductible asset impairment charge |  | $ 400 |  | $ 400 |  |
Income benefit | $ (7,331) | $ (14,126) | $ (13,711) | (22,254) |  |
Minimum |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Expected annual effective tax rate in future periods |  |  | 26.00% |  |  |
Maximum |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Expected annual effective tax rate in future periods |  |  | 28.00% |  |  |
Dealership |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Percentage of dealership that is accounted for under the equity method | 50.00% |  | 50.00% |  |  |
ASU 2014-09 | Finance, insurance and other, net |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Contract assets | $ 8,000 |  | $ 8,000 |  |  |
ASU 2016-09 |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Income benefit |  |  |  | $ 500 |  |

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