Condensed Consolidated Financial Information Condensed Consolidated Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 198,925	$ 384,857	$ 141,047
Cash paid in acquisitions, net of cash received	(109,081)	(57,327)	(212,252)
Proceeds from disposition of franchises, property and equipment	10,708	36,843	41,581
Purchases of property and equipment, including real estate	(215,832)	(156,521)	(120,252)
Payments for (Proceeds from) Other Investing Activities	1,607	2,965	6,421
Net Cash Provided by (Used in) Investing Activities	(312,598)	(174,040)	(284,502)
Borrowings on credit facility - floorplan line and other	7,019,070	6,597,406	7,557,237
Repayments On Credit Facility Floorplan Line	(6,957,866)	(6,676,161)	(7,504,516)
Borrowings on Credit Facility Acquisition Line	68,086	220,020	489,548
Repayments on Credit Facility Acquisition Line	(42,278)	(220,020)	(557,696)
Net borrowings on 5.25% Senior Unsecured Notes	0	0	296,250
Payments of Debt Issuance Costs		(3,513)	(788)
Proceeds from Issuance of Other Long-term Debt	165,702	49,972	59,855
Repayments of Other Long-term Debt	(121,199)	(45,928)	(63,769)
Borrowings Of Long Term Debt Related To Real Estate Loans	75,309	42,654	32,026
Borrowings Of Long Term Debt Related To Real Estate Loans, Net of Debt Issue Costs		39,141	31,238
Principal Payments Of Long Term Debt Related To Real Estate Loans	(29,391)	(25,463)	(72,079)
Net Issuance of Common and Treasury Shares to Employee Stock Compensation Plans	4,603	3,868	214
Repurchases of common stock, amounts based on settlement date	(40,094)	(127,606)	(97,473)
Tax effect from excess stock-based compensation		(249)	2,142
Dividends paid	(20,466)	(19,987)	(19,942)
Borrowings (repayments) with subsidiaries	0	0	0
Change in investment in subsidiaries	0	0	0
Net cash provided by (used in) financing activities	121,476	(205,007)	121,009
Effect of Exchange Rate on Cash and Cash Equivalents	(8)	2,145	(5,492)
Cash and Cash Equivalents, Period Increase (Decrease)	7,795	7,955	(27,938)
Cash and Cash Equivalents, at Carrying Value	28,787	20,992	13,037	$ 40,975
Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(1,911)	(760)	(2,662)
Cash paid in acquisitions, net of cash received	(46,607)	(57,327)	0
Proceeds from disposition of franchises, property and equipment	2,363	1,526	748
Purchases of property and equipment, including real estate	(30,490)	(18,258)	(23,243)
Payments for (Proceeds from) Other Investing Activities	0	217	0
Net Cash Provided by (Used in) Investing Activities	(74,734)	(73,842)	(22,495)
Borrowings on credit facility - floorplan line and other	0	0	0
Repayments On Credit Facility Floorplan Line	0	0	0
Borrowings on Credit Facility Acquisition Line	0	0	0
Repayments on Credit Facility Acquisition Line	0	0	0
Net borrowings on 5.25% Senior Unsecured Notes			0
Payments of Debt Issuance Costs		0	0
Proceeds from Issuance of Other Long-term Debt	140,629	49,972	59,404
Repayments of Other Long-term Debt	(120,168)	(45,005)	(62,383)
Borrowings Of Long Term Debt Related To Real Estate Loans	28,890	0	22,430
Principal Payments Of Long Term Debt Related To Real Estate Loans	(6,460)	(5,154)	(3,845)
Net Issuance of Common and Treasury Shares to Employee Stock Compensation Plans	0	0	0
Repurchases of common stock, amounts based on settlement date	0	0	0
Tax effect from excess stock-based compensation		0	0
Dividends paid	0	0	0
Borrowings (repayments) with subsidiaries	29,827	7,737	(9,045)
Change in investment in subsidiaries	9,673	71,161	15,191
Net cash provided by (used in) financing activities	82,391	78,711	21,752
Effect of Exchange Rate on Cash and Cash Equivalents	(8)	2,145	(5,492)
Cash and Cash Equivalents, Period Increase (Decrease)	5,738	6,254	(8,897)
Cash and Cash Equivalents, at Carrying Value	18,691	12,953	6,699	15,596
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(13,759)	238,552	49,710
Cash paid in acquisitions, net of cash received	(62,474)	0	(212,252)
Proceeds from disposition of franchises, property and equipment	8,345	35,317	40,833
Purchases of property and equipment, including real estate	(185,342)	(138,263)	(97,009)
Payments for (Proceeds from) Other Investing Activities	1,607	2,748	6,421
Net Cash Provided by (Used in) Investing Activities	(237,864)	(100,198)	(262,007)
Borrowings on credit facility - floorplan line and other	7,019,070	6,597,406	7,557,237
Repayments On Credit Facility Floorplan Line	(6,957,866)	(6,676,161)	(7,504,516)
Borrowings on Credit Facility Acquisition Line	0	0	0
Repayments on Credit Facility Acquisition Line	0	0	0
Net borrowings on 5.25% Senior Unsecured Notes			0
Payments of Debt Issuance Costs		(516)	(788)
Proceeds from Issuance of Other Long-term Debt	19	0	451
Repayments of Other Long-term Debt	(718)	(923)	(1,386)
Borrowings Of Long Term Debt Related To Real Estate Loans	46,419	42,654	9,596
Principal Payments Of Long Term Debt Related To Real Estate Loans	(22,931)	(20,309)	(68,234)
Net Issuance of Common and Treasury Shares to Employee Stock Compensation Plans	0	0	0
Repurchases of common stock, amounts based on settlement date	0	0	0
Tax effect from excess stock-based compensation		0	2,142
Dividends paid	0	0	0
Borrowings (repayments) with subsidiaries	(32,719)	(406,888)	(211,236)
Change in investment in subsidiaries	202,406	328,084	409,990
Net cash provided by (used in) financing activities	253,680	(136,653)	193,256
Effect of Exchange Rate on Cash and Cash Equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	2,057	1,701	(19,041)
Cash and Cash Equivalents, at Carrying Value	10,096	8,039	6,338	25,379
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	214,595	147,065	93,999
Cash paid in acquisitions, net of cash received	0	0	0
Proceeds from disposition of franchises, property and equipment	0	0	0
Purchases of property and equipment, including real estate	0	0	0
Payments for (Proceeds from) Other Investing Activities	0	0	0
Net Cash Provided by (Used in) Investing Activities	0	0	0
Borrowings on credit facility - floorplan line and other	0	0	0
Repayments On Credit Facility Floorplan Line	0	0	0
Borrowings on Credit Facility Acquisition Line	68,086	220,020	489,548
Repayments on Credit Facility Acquisition Line	(42,278)	(220,020)	(557,696)
Net borrowings on 5.25% Senior Unsecured Notes			(296,250)
Payments of Debt Issuance Costs		(2,997)	0
Proceeds from Issuance of Other Long-term Debt	25,054	0	0
Repayments of Other Long-term Debt	(313)	0	0
Borrowings Of Long Term Debt Related To Real Estate Loans	0	0	0
Principal Payments Of Long Term Debt Related To Real Estate Loans	0	0	0
Net Issuance of Common and Treasury Shares to Employee Stock Compensation Plans	4,603	3,868	214
Repurchases of common stock, amounts based on settlement date	(40,094)	(127,606)	(97,473)
Tax effect from excess stock-based compensation		(249)	0
Dividends paid	(20,466)	(19,987)	(19,942)
Borrowings (repayments) with subsidiaries	2,892	399,151	220,281
Change in investment in subsidiaries	(212,079)	(399,245)	(425,181)
Net cash provided by (used in) financing activities	(214,595)	(147,065)	(93,999)
Effect of Exchange Rate on Cash and Cash Equivalents	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	0	0	0
Cash and Cash Equivalents, at Carrying Value	$ 0	$ 0	$ 0	$ 0