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Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Discrete charge for non-deductible executive compensation, transition costs |  | $ 800 |  | $ 1,500 | $ 800
Effective Income Tax Rate Reconciliation, Tax Settlement, State and Local, Amount |  | $ 400 |  | $ 400 |
Discrete charge for non-deductible disposition |  |  |  |  | $ 600
Percentage of dealership that is accounted for under the equity method | 50.00% | 50.00% |  | 50.00% |
Contract work in process | $ 4,700 |  |  | $ 4,800 |
Effective tax rate from continuing operations |  | 28.00% | 32.40% | 29.20% | 31.10%
Tax expense for uncertain tax positions |  |  |  | $ 200 | $ 200
Discrete benefit related to vested or exercised stock compensation |  |  |  | 200 | 900
Income benefit |  | $ (11,372) | $ (7,331) | (40,430) | $ (13,711)
Effective Income Tax Rate Reconciliation, Tax Settlement, State and Local, Amount |  | $ 400 |  | $ 400 |
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 | $ 5,400 | $ 5,900 |  | $ 5,900 |

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