Interim Financial Information (Details Textual) $ in Thousands		3 Months Ended
	Jan. 01, 2018 USD ($)	Mar. 31, 2018 USD ($) dealerships town states	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business And Organization [Line Items]
Value of used vehicle inventory financed		85.00%
Parts And Service Sales		$ 349,515	$ 319,698
Accounts, Notes, Loans and Financing Receivable, Net, Current	$ 208,917	200,159		$ 188,611
Inventory, Net	(1,759,633)	(1,804,176)		(1,763,293)
Accounts Payable, Current	414,737	491,841		412,981
Deferred Tax Liabilities, Net, Noncurrent	127,897	134,800		124,404
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	11,397
Retained Earnings (Accumulated Deficit)	1,257,720	1,288,052		1,246,323
Cash and Cash Equivalents, at Carrying Value		$ 33,090		28,787	$ 24,246
Number of International Regions		2
Number of Reportable Segments		3
Restricted Cash and Cash Equivalents		$ 34,559	34,680	29,631	$ 24,246
Financial Services Revenue		112,322	96,834
Parts And Service Sales Cost Of Sales		162,651	147,342
Selling, General and Administrative Expense		(324,347)	(289,779)
Income Tax Expense (Benefit)		10,353	17,257
Net Income (Loss) Attributable to Parent		35,814	33,939
Accrued Liabilities, Current		(194,248)		(177,070)
Interest Paid		20,300	17,600
Proceeds from Income Tax Refunds		400	300
BRAZIL
Business And Organization [Line Items]
Parts And Service Sales		$ 11,860	11,758
Number of States in which Entity Operates | states		4
Number of Dealerships | dealerships		16
Financial Services Revenue		$ 1,872	1,987
Income Tax Expense (Benefit)		134	40
Net Income (Loss) Attributable to Parent		(214)	169
UNITED STATES
Business And Organization [Line Items]
Parts And Service Sales		$ 284,514	271,159
Number of States in which Entity Operates | states		15
Number of Dealerships | dealerships		117
Financial Services Revenue		$ 96,187	85,819
Income Tax Expense (Benefit)		9,357	16,347
Net Income (Loss) Attributable to Parent		31,153	29,259
UNITED KINGDOM
Business And Organization [Line Items]
Parts And Service Sales		$ 53,141	36,781
Number of Towns in which Entity Operates | town		32
Number of Dealerships | dealerships		47
Financial Services Revenue		$ 14,263	9,028
Income Tax Expense (Benefit)		862	870
Net Income (Loss) Attributable to Parent		4,875	4,511
Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Business And Organization [Line Items]
Investments, Fair Value Disclosure		1,469	$ 844	$ 844
Accounting Standards Update 2014-09 [Member]
Business And Organization [Line Items]
Parts And Service Sales		350,992
Accounts, Notes, Loans and Financing Receivable, Net, Current		181,131
Inventory, Net		(1,807,371)
Accounts Payable, Current		490,281
Deferred Tax Liabilities, Net, Noncurrent		131,459
Retained Earnings (Accumulated Deficit)		1,277,120
Financial Services Revenue		112,122
Parts And Service Sales Cost Of Sales		163,116
Selling, General and Administrative Expense		(324,543)
Income Tax Expense (Benefit)		10,504
Net Income (Loss) Attributable to Parent		36,279
Accounting Standards Update 2014-09 [Member] | PartsandServiceSales606 [Domain]
Business And Organization [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	4,800
Accounting Standards Update 2014-09 [Member] | FinanceandInsuranceSales606 [Domain]
Business And Organization [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	6,600
Accounts Receivable [Member]
Business And Organization [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	20,306
Inventories [Member]
Business And Organization [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(3,660)
Accounts Payable [Member]
Business And Organization [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	1,756
Other Noncurrent Liabilities [Member]
Business And Organization [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 3,493
Accounting Standards Update 2014-09 [Member]
Business And Organization [Line Items]
Parts And Service Sales		(1,477)
Accounts, Notes, Loans and Financing Receivable, Net, Current		19,028
Inventory, Net		(3,195)
Accounts Payable, Current		1,560
Deferred Tax Liabilities, Net, Noncurrent		3,341
Retained Earnings (Accumulated Deficit)		10,932
Financial Services Revenue		200
Parts And Service Sales Cost Of Sales		(465)
Selling, General and Administrative Expense		(196)
Income Tax Expense (Benefit)		(151)
Net Income (Loss) Attributable to Parent		$ (465)