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Financial Instruments and Fair Value Measurements (Narrative) (Details) - USD ($) | 3 Months Ended | 4 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2017 | Apr. 30, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Franchise rights impairment |  |  | $ 0 | $ 0 | $ 15,400,000
Net adjustments and impairment of assets held for sale | $ 26,200,000 |  |  |  |
Nonrecurring [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Goodwill, Impairment Loss |  |  | 0 |  |
Net adjustments and impairment of assets held for sale |  |  | $ 26,000,000 | $ 12,800,000 |
Goodwill [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Date of annual goodwill and indefinite lived intangible assets impairment test |  |  | April 30 | April 30 | April 30
Franchise Rights [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Date of annual goodwill and indefinite lived intangible assets impairment test |  |  | April 30 | April 30 | April 30
Franchise Rights [Member] | Nonrecurring [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Franchise rights impairment |  | $ 0 | $ 0 | $ 0 |
Franchise Rights [Member] | Nonrecurring [Member] | Volkswagen [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Franchise rights impairment |  |  |  |  | $ 15,400,000
Continuing Operations [Member] | Nonrecurring [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Impairment of long-lived assets held and used |  |  | 400,000 | 1,900,000 |
Net adjustments and impairment of assets held for sale |  |  | 26,000,000 | 12,100,000 |
Discontinued Operations [Member] | Nonrecurring [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Impairment of assets for sale |  |  | 0 | 700,000 |
Reported Value Measurement [Member] | Continuing Operations [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets held for sale | 169,100,000 |  | 169,100,000 | 41,400,000 |
Reported Value Measurement [Member] | Discontinued Operations [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets held for sale | $ 14,400,000 |  | $ 14,400,000 | $ 15,700,000 |

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