Credit Facilities (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Credit Facility (Textual) [Abstract]
Offset account related to floorplan notes payable - credit facility	$ (86,547)	$ (86,547)	$ (59,626)
Maximum Limit of Restricted Payment		the sum of $208.5 million plus (or minus if negative) (a) one-half of the aggregate consolidated net income for the period beginning on April 1, 2014 and ending on the date of determination and (b) the amount of net cash proceeds received from the sale of capital stock after June 2, 2014 and ending on the date of determination less (c) cash dividends and share repurchases after June 2, 2014
Floorplan notes payable - manufacturer affiliates	397,183	$ 397,183	392,661
FMCC Offset	22,500	22,500	$ 25,500
Revolving Credit Facility [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	$ 1,800,000	$ 1,800,000
Line of Credit Facility, Expiration Date	Jun. 17, 2021
Number of financial institutions	24	24
Number of Manufacturer-affiliated finance companies	6	6
Number of tranches	2	2
Line of credit facility, maximum borrowing capacity can be extended, amount	$ 2,100,000	$ 2,100,000
Line of credit facility, unamortized cost	4,200	4,200
Restricted Payment Basket	184,800	184,800
Revolving Credit Facility, Floorplan Line [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	1,750,000	$ 1,750,000
Maximum period for outstanding borrowing		1 year
Commitment fees, Percentage		0.15%
Line of Credit Facility, Amount Outstanding	1,133,296	$ 1,133,296
Available amount under borrowing capacity	$ 306,700	$ 306,700
Weighted average interest rate	2.70%	2.70%	2.00%
Revolving Credit Facility, Floorplan Line, New Vehicles [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		1.25%
Revolving Credit Facility, Floorplan Line, Used Vehicles [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		1.50%
Revolving Credit Facility, Acquisition Line [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	$ 360,000	$ 360,000
Line of credit facility minimum borrowing capacity	50,000	$ 50,000
Basis spread on interest rate		1.50%
Restricted payment maximum	50,000	$ 50,000
Line of Credit Facility, Amount Outstanding	26,988	26,988	$ 0
Available amount under borrowing capacity	308,200	308,200
Letters of credit outstanding	$ 25,000	$ 25,000
Debt interest rate	2.30%	2.30%
Revolving Credit Facility, Acquisition Line [Member] | Maximum [Member]
Credit Facility (Textual) [Abstract]
Commitment fees, Percentage		0.45%
Revolving Credit Facility, Acquisition Line [Member] | Minimum [Member]
Credit Facility (Textual) [Abstract]
Commitment fees, Percentage		0.20%
Revolving Credit Facility, Acquisition Line [Member] | United States of America, Dollars | Maximum [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		1.00%
Revolving Credit Facility, Acquisition Line [Member] | United States of America, Dollars | Minimum [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		0.00%
Revolving Credit Facility, Acquisition Line [Member] | Euros or Pound Sterling [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	$ 125,000	$ 125,000
Revolving Credit Facility, Acquisition Line [Member] | Euros or Pound Sterling [Member] | Maximum [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		2.50%
Revolving Credit Facility, Acquisition Line [Member] | Euros or Pound Sterling [Member] | Minimum [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		1.25%
FMCC Facility [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	300,000	$ 300,000
Available amount under borrowing capacity	169,500	$ 169,500
Cancellation of agreement		30 days
Floorplan notes payable - manufacturer affiliates	$ 130,484	$ 130,484
Debt interest rate	6.00%	6.00%	5.25%
UK Credit Facilities [Member]
Credit Facility (Textual) [Abstract]
Line of Credit Facility, Amount Outstanding	$ 122,800	$ 122,800
UK Credit Facilities [Member] | Maximum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	3.95%	3.95%
UK Credit Facilities [Member] | Minimum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	1.25%	1.25%
Brazilian Credit Facility [Member] | Maximum [Member]
Credit Facility (Textual) [Abstract]
Line of Credit Facility, Amount Outstanding	$ 22,700	$ 22,700
Debt interest rate	18.02%	18.02%
Brazilian Credit Facility [Member] | Minimum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	11.42%	11.42%
Rental Vehicle Credit Facility [Member] | Maximum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	6.00%	6.00%
Debt Instrument Maturity Date Period		2 years
FMCC Facility [Member]
Credit Facility (Textual) [Abstract]
Basis spread on interest rate		1.50%
Floorplan notes payable - manufacturer affiliates	$ 130,484	$ 130,484	$ 149,744
Rental Vehicle Credit Facility [Member]
Credit Facility (Textual) [Abstract]
Line of Credit Facility, Amount Outstanding	$ 119,600	$ 119,600