Summary of Significant Accounting Policies and Estimates Summary of Significant Account Policies and Estimates (Details Textuals)	3 Months Ended						12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies and Estimates [Line Items]
Value of used vehicle inventory financed							85.00%
Number of Reportable Segments							3
Change in the historical chargeback results used in determining estimates of future amounts	10.00%						10.00%
Change in the reserve of future amounts	$ 5,000,000						$ 5,000,000
Restricted cash and short term investments	109,000,000		$ 85,100,000				109,000,000	$ 85,100,000
Inventory cost reduced for interest assistance received from manufacturers	9,100,000		9,600,000				9,100,000	9,600,000
Reduction in new vehicle cost of sales	$ 48,900,000		49,200,000				$ 48,900,000	$ 49,200,000	$ 50,500,000
Number of geographic regions							3	4
Weighted Income approach to determine the fair value of the Company's reporting units	80.00%						80.00%
Weighted Market approach to determine the fair value of the Company's reporting units	20.00%						20.00%
Advertising expenses							$ 74,100,000	$ 75,300,000	74,600,000
Reduction in advertising expenses							$ 15,300,000	16,700,000	17,300,000
Percentage of Company's new vehicle sales volume more than which no other manufacturer accounted for							2.90%
Accounts Receivable, Gross, Current	$ 191,749,000		176,260,000				$ 191,749,000	176,260,000
Interest paid							117,100,000	109,300,000	92,000,000
Income taxes refundable							$ 61,000,000	56,900,000	74,800,000
Percentage of change in loss reserve due to change in actuarial loss rate per employee	10.00%						10.00%
Change in loss reserve due to change in actuarial loss rate per employee	$ 2,100,000						$ 2,100,000
Maximum payout under first layer							0
Limited exposure in no stop loss plan per occurrence							1,000,000
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims							20,500,000
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)	$ 9,800,000	$ 9,500,000	19,200,000	$ 10,600,000	$ 200,000		$ 19,300,000	30,000,000	$ 30,100,000
Used vehicle days supply							39 days
FCA US [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							3.90%
Share in company receivable balance	3.40%						3.40%
Toyota [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							25.30%
Share in company receivable balance	16.60%						16.60%
BMW [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							12.70%
Share in company receivable balance	14.10%						14.10%
Ford [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							11.50%
Share in company receivable balance	13.50%						13.50%
Daimler [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							4.00%
Share in company receivable balance	9.00%						9.00%
General Motors [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							6.20%
Share in company receivable balance	14.00%						14.00%
Nissan [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							7.40%
Share in company receivable balance	5.00%						5.00%
Honda [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							9.20%
Share in company receivable balance	3.20%						3.20%
Hyundai [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							3.90%
Share in company receivable balance	3.80%						3.80%
Volkswagen [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume							13.00%
Share in company receivable balance	11.20%						11.20%
5.00% Senior Note [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Unsecured Long-term Debt, Noncurrent	$ 542,063,000		540,465,000				$ 542,063,000	540,465,000
Long-term Debt, Fair Value	567,900,000		548,400,000				567,900,000	548,400,000
5.25% Senior Note [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Unsecured Long-term Debt, Noncurrent	296,151,000		295,591,000				296,151,000	295,591,000
Long-term Debt, Fair Value	310,900,000		297,000,000				310,900,000	297,000,000
Real Estate Related and Other Long Term Debt [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Other Long-term Debt	$ 440,845,000		385,358,000				440,845,000	385,358,000
Maximum [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Interest assistance received related to vehicles sold				139.90%
Per Occurrence Company Deductible							10,000,000
Aggregate deductible							$ 30,000,000
Minimum [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Interest assistance received related to vehicles sold						88.00%
U.S.
Summary of Significant Accounting Policies and Estimates [Line Items]
Company operates in different states	15						15
Amounts Due From Manufacturers [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Accounts Receivable, Gross, Current	$ 109,599,000		$ 95,754,000				$ 109,599,000	$ 95,754,000
Scenario, Forecast [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Recovery back to normalized levels by 2016										16,500,000	16,700,000	16,900,000