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Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Parenthetical) (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
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Statement of Financial Position [Abstract] |  |
Accumulated depreciation | $ 380.5 | $ 347.3
Offset account related to floorplan notes payable - credit facility | 25.0 | 33.6
Offset account related to floorplan notes payable - manufacturer affiliates | $ 0.2 | $ 0.1

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