Condensed Consolidated Financial Information Condensed Consolidated Cash Flow (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 230,868	$ 271,836
Cash paid in acquisitions, net of cash received	(212,252)	(309,257)
Proceeds from disposition of franchises, property and equipment	9,684	138,800
Purchases of property and equipment, including real estate	(78,339)	(91,345)
Other	6,047	(5,832)
Net cash used in investing activities	(274,860)	(267,634)
Borrowings on credit facility - floorplan line and other	5,529,338	6,047,392
Repayments on credit facility - floorplan line and other	(5,479,152)	(6,086,414)
Borrowings on credit facility - acquisition line	584,643	314,963
Repayment on credit facility - acquisition line	(515,944)	(374,989)
Borrowings On Real Estate Credit Facility	0	200
Principal Payments On Real Estate Credit Facility	(2,505)	(9,081)
Proceeds from Issuance of Unsecured Debt	0	539,600
Payments of Debt Issuance Costs	0	1,881
Repayments of 3.00% Convertible Notes	0	260,074
Proceeds from call options and warrants related to 3.00% Notes	0	32,697
Repayments of 2.25% Convertible Notes	0	(182,756)
Borrowings on other debt	33,375	78,710
Principal payments on other debt	(42,929)	(70,267)
Borrowings on debt related to real estate	22,430	65,628
Principal payments on debt related to real estate	(18,536)	(39,024)
Employee stock purchase plan purchases, net of employee tax withholdings	(789)	187
Repurchases of common stock, amounts based on settlement date	(66,746)	(16,947)
Tax effect from stock-based compensation	1,827	1,145
Dividends paid	(14,781)	(12,291)
Borrowings (repayments) with subsidiaries	0	0
Investment in subsidiaries	0	0
Distributions to parent		0
Net cash provided by (used in) financing activities	30,231	26,798
Effect of Exchange Rate on Cash and Cash Equivalents	(5,246)	(563)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(19,007)	30,437
Cash and cash equivalents	21,968	50,652	$ 40,975	$ 20,215
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	127,385	74,327
Cash paid in acquisitions, net of cash received	0	0
Proceeds from disposition of franchises, property and equipment	0	0
Purchases of property and equipment, including real estate	0	0
Other	0	0
Net cash used in investing activities	0	0
Borrowings on credit facility - floorplan line and other	0	0
Repayments on credit facility - floorplan line and other	0	0
Borrowings on credit facility - acquisition line	584,643	314,963
Repayment on credit facility - acquisition line	(515,944)	(374,989)
Borrowings On Real Estate Credit Facility		0
Principal Payments On Real Estate Credit Facility	0	0
Proceeds from Issuance of Unsecured Debt		539,600
Payments of Debt Issuance Costs		1,881
Repayments of 3.00% Convertible Notes		260,074
Proceeds from call options and warrants related to 3.00% Notes		32,697
Repayments of 2.25% Convertible Notes		(182,756)
Borrowings on other debt	0	0
Principal payments on other debt	0	0
Borrowings on debt related to real estate	0	0
Principal payments on debt related to real estate	0	0
Employee stock purchase plan purchases, net of employee tax withholdings	(789)	187
Repurchases of common stock, amounts based on settlement date	(66,746)	(16,947)
Tax effect from stock-based compensation	0	0
Dividends paid	(14,781)	(12,291)
Borrowings (repayments) with subsidiaries	85,465	87,136
Investment in subsidiaries	(199,233)	(199,972)
Distributions to parent		0
Net cash provided by (used in) financing activities	(127,385)	(74,327)
Effect of Exchange Rate on Cash and Cash Equivalents	0	26
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	0	26
Cash and cash equivalents	0	26	0	0
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	93,518	204,887
Cash paid in acquisitions, net of cash received	(212,252)	(306,467)
Proceeds from disposition of franchises, property and equipment	8,986	138,546
Purchases of property and equipment, including real estate	(61,052)	(85,239)
Other	6,047	(5,832)
Net cash used in investing activities	(258,271)	(258,992)
Borrowings on credit facility - floorplan line and other	5,529,338	6,047,392
Repayments on credit facility - floorplan line and other	(5,479,152)	(6,086,414)
Borrowings on credit facility - acquisition line	0	0
Repayment on credit facility - acquisition line	0	0
Borrowings On Real Estate Credit Facility		200
Principal Payments On Real Estate Credit Facility	(2,505)	(9,081)
Proceeds from Issuance of Unsecured Debt		0
Payments of Debt Issuance Costs		0
Repayments of 3.00% Convertible Notes		0
Proceeds from call options and warrants related to 3.00% Notes		0
Repayments of 2.25% Convertible Notes		0
Borrowings on other debt	460	0
Principal payments on other debt	(1,157)	0
Borrowings on debt related to real estate	0	52,279
Principal payments on debt related to real estate	(15,843)	(29,458)
Employee stock purchase plan purchases, net of employee tax withholdings	0	0
Repurchases of common stock, amounts based on settlement date	0	0
Tax effect from stock-based compensation	1,827	1,145
Dividends paid	0	0
Borrowings (repayments) with subsidiaries	(73,365)	(94,311)
Investment in subsidiaries	184,168	200,094
Distributions to parent		2,118
Net cash provided by (used in) financing activities	143,771	83,964
Effect of Exchange Rate on Cash and Cash Equivalents	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(20,982)	29,859
Cash and cash equivalents	4,397	34,165	25,379	4,306
Non-Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	9,965	(7,378)
Cash paid in acquisitions, net of cash received	0	(2,790)
Proceeds from disposition of franchises, property and equipment	698	254
Purchases of property and equipment, including real estate	(17,287)	(6,106)
Other	0	0
Net cash used in investing activities	(16,589)	(8,642)
Borrowings on credit facility - floorplan line and other	0	0
Repayments on credit facility - floorplan line and other	0	0
Borrowings on credit facility - acquisition line	0	0
Repayment on credit facility - acquisition line	0	0
Borrowings On Real Estate Credit Facility		0
Principal Payments On Real Estate Credit Facility	0	0
Proceeds from Issuance of Unsecured Debt		0
Payments of Debt Issuance Costs		0
Repayments of 3.00% Convertible Notes		0
Proceeds from call options and warrants related to 3.00% Notes		0
Repayments of 2.25% Convertible Notes		0
Borrowings on other debt	32,915	78,710
Principal payments on other debt	(41,772)	(70,267)
Borrowings on debt related to real estate	22,430	13,349
Principal payments on debt related to real estate	(2,693)	(9,566)
Employee stock purchase plan purchases, net of employee tax withholdings	0	0
Repurchases of common stock, amounts based on settlement date	0	0
Tax effect from stock-based compensation	0	0
Dividends paid	0	0
Borrowings (repayments) with subsidiaries	(12,100)	7,175
Investment in subsidiaries	15,065	(122)
Distributions to parent		(2,118)
Net cash provided by (used in) financing activities	13,845	17,161
Effect of Exchange Rate on Cash and Cash Equivalents	(5,246)	(589)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	1,975	552
Cash and cash equivalents	17,571	$ 16,461	15,596	$ 15,909
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 0		$ 0