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