Condensed Consolidated Financial Information Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Asset Impairment Charges	$ 1,039	$ 1,721	$ 1,039	$ 1,721
Cash and Cash Equivalents, at Carrying Value	24,225	21,295	24,225	21,295	$ 40,975	$ 20,215
Contracts In Transit And Vehicle Receivables Net	233,888		233,888		237,448
Accounts, Notes, Loans and Financing Receivable, Net, Current	144,265		144,265		151,330
Intercompany accounts receivable current	0		0		0
Inventories, net	1,657,105		1,657,105		1,556,705
Deferred Tax Assets, Net, Current	12,031		12,031		11,062
Prepaid Expense and Other Assets, Current	27,851		27,851		37,699
Total current assets	2,099,365		2,099,365		2,035,219
Property, Plant and Equipment, Net	965,363		965,363		950,388
Goodwill	887,200		887,200		830,377
Indefinite-Lived Franchise Rights	331,811		331,811		303,947
Investment in Subsidiaries	0		0		0
Other Assets, Noncurrent	19,235		19,235		21,561
Total assets	4,302,974		4,302,974		4,141,492
Floorplan notes payable - credit facility	1,205,729		1,205,729		1,143,246
Offset account related to floorplan notes payable - credit facility	(22,466)		(22,466)		(39,616)
Floorplan notes payable - manufacturer affiliates	308,710		308,710		307,656
FMCC Offset	(23,300)		(23,300)		(22,500)
Long-term Debt and Capital Lease Obligations, Current	76,442		76,442		72,630
Accounts Payable, Current	304,361		304,361		288,320
Intercompany accounts payable current	0		0		0
Accrued Liabilities, Current	161,123		161,123		172,463
Total current liabilities	2,010,599		2,010,599		1,922,199
LONG-TERM DEBT, net of current maturities	1,041,852		1,041,852		1,008,837
Derivative Liability, Noncurrent	29,020		29,020		25,311
Deferred Income Taxes and Other Liabilities, Noncurrent	217,352		217,352		207,135
Stockholders' Equity Attributable to Parent	1,004,151		1,004,151		978,010
Intercompany note receivable	0		0		0
Stockholders' Equity Attributable to Parent Excluding Intercompany Receivables	1,004,151		1,004,151		978,010
Total liabilities and stockholders’ equity	4,302,974		4,302,974		4,141,492
Parent Company [Member]
Asset Impairment Charges	0	0	0	0
Cash and Cash Equivalents, at Carrying Value	0	494	0	494	0	0
Contracts In Transit And Vehicle Receivables Net	0		0		0
Accounts, Notes, Loans and Financing Receivable, Net, Current	0		0		0
Intercompany accounts receivable current	0		0		0
Inventories, net	0		0		0
Deferred Tax Assets, Net, Current	331		331		196
Prepaid Expense and Other Assets, Current	311		311		590
Total current assets	642		642		786
Property, Plant and Equipment, Net	0		0		0
Goodwill	0		0		0
Indefinite-Lived Franchise Rights	0		0		0
Investment in Subsidiaries	2,102,908		2,102,908		1,964,442
Other Assets, Noncurrent	0		0		0
Total assets	2,103,550		2,103,550		1,965,228
Floorplan notes payable - credit facility	0		0		0
Offset account related to floorplan notes payable - credit facility	0		0		0
Floorplan notes payable - manufacturer affiliates	0		0		0
FMCC Offset	0		0		0
Long-term Debt and Capital Lease Obligations, Current	0		0		0
Accounts Payable, Current	0		0		0
Intercompany accounts payable current	364,672		364,672		295,421
Accrued Liabilities, Current	0		0		0
Total current liabilities	364,672		364,672		295,421
LONG-TERM DEBT, net of current maturities	631,387		631,387		609,812
Derivative Liability, Noncurrent	0		0		0
Deferred Income Taxes and Other Liabilities, Noncurrent	0		0		0
Stockholders' Equity Attributable to Parent	1,107,491		1,107,491		1,059,995
Intercompany note receivable	0		0		0
Stockholders' Equity Attributable to Parent Excluding Intercompany Receivables	1,107,491		1,107,491		1,059,995
Total liabilities and stockholders’ equity	2,103,550		2,103,550		1,965,228
Guarantor Subsidiaries [Member]
Asset Impairment Charges	498	1,721	498	1,721
Cash and Cash Equivalents, at Carrying Value	4,620	3,831	4,620	3,831	25,379	4,306
Contracts In Transit And Vehicle Receivables Net	202,435		202,435		218,361
Accounts, Notes, Loans and Financing Receivable, Net, Current	115,817		115,817		117,427
Intercompany accounts receivable current	249,576		249,576		276,217
Inventories, net	1,438,449		1,438,449		1,342,022
Deferred Tax Assets, Net, Current	11,700		11,700		10,866
Prepaid Expense and Other Assets, Current	15,356		15,356		22,039
Total current assets	2,037,953		2,037,953		2,012,311
Property, Plant and Equipment, Net	849,407		849,407		839,063
Goodwill	769,163		769,163		700,642
Indefinite-Lived Franchise Rights	290,876		290,876		257,502
Investment in Subsidiaries	0		0		0
Other Assets, Noncurrent	9,120		9,120		10,120
Total assets	3,956,519		3,956,519		3,819,638
Floorplan notes payable - credit facility	1,204,346		1,204,346		1,137,743
Offset account related to floorplan notes payable - credit facility	(22,466)		(22,466)		(39,616)
Floorplan notes payable - manufacturer affiliates	219,148		219,148		207,329
FMCC Offset	(23,300)		(23,300)		(22,500)
Long-term Debt and Capital Lease Obligations, Current	59,379		59,379		61,185
Accounts Payable, Current	173,603		173,603		176,143
Intercompany accounts payable current	0		0		0
Accrued Liabilities, Current	136,583		136,583		149,700
Total current liabilities	1,747,293		1,747,293		1,669,984
LONG-TERM DEBT, net of current maturities	340,496		340,496		347,202
Derivative Liability, Noncurrent	29,020		29,020		25,311
Deferred Income Taxes and Other Liabilities, Noncurrent	204,703		204,703		193,077
Stockholders' Equity Attributable to Parent	1,999,679		1,999,679		1,879,485
Intercompany note receivable	(364,672)		(364,672)		(295,421)
Stockholders' Equity Attributable to Parent Excluding Intercompany Receivables	1,635,007		1,635,007		1,584,064
Total liabilities and stockholders’ equity	3,956,519		3,956,519		3,819,638
Non-Guarantor Subsidiaries [Member]
Asset Impairment Charges	541	0	541	0
Cash and Cash Equivalents, at Carrying Value	19,605	16,970	19,605	16,970	15,596	$ 15,909
Contracts In Transit And Vehicle Receivables Net	31,453		31,453		19,087
Accounts, Notes, Loans and Financing Receivable, Net, Current	28,448		28,448		33,903
Intercompany accounts receivable current	0		0		0
Inventories, net	218,656		218,656		214,683
Deferred Tax Assets, Net, Current	0		0		0
Prepaid Expense and Other Assets, Current	12,184		12,184		15,070
Total current assets	310,346		310,346		298,339
Property, Plant and Equipment, Net	115,956		115,956		111,325
Goodwill	118,037		118,037		129,735
Indefinite-Lived Franchise Rights	40,935		40,935		46,445
Investment in Subsidiaries	0		0		0
Other Assets, Noncurrent	10,115		10,115		11,441
Total assets	595,389		595,389		597,285
Floorplan notes payable - credit facility	1,383		1,383		5,503
Offset account related to floorplan notes payable - credit facility	0		0		0
Floorplan notes payable - manufacturer affiliates	89,562		89,562		100,327
FMCC Offset	0		0		0
Long-term Debt and Capital Lease Obligations, Current	17,063		17,063		11,445
Accounts Payable, Current	130,758		130,758		112,177
Intercompany accounts payable current	249,576		249,576		276,217
Accrued Liabilities, Current	24,540		24,540		22,763
Total current liabilities	512,882		512,882		528,432
LONG-TERM DEBT, net of current maturities	69,969		69,969		51,823
Derivative Liability, Noncurrent	0		0		0
Deferred Income Taxes and Other Liabilities, Noncurrent	12,649		12,649		14,058
Stockholders' Equity Attributable to Parent	(111)		(111)		2,972
Intercompany note receivable	0		0		0
Stockholders' Equity Attributable to Parent Excluding Intercompany Receivables	(111)		(111)		2,972
Total liabilities and stockholders’ equity	595,389		595,389		597,285
Consolidation, Eliminations [Member]
Asset Impairment Charges	0	$ 0	0	$ 0
Cash and Cash Equivalents, at Carrying Value	0		0		0
Contracts In Transit And Vehicle Receivables Net	0		0		0
Accounts, Notes, Loans and Financing Receivable, Net, Current	0		0		0
Intercompany accounts receivable current	(249,576)		(249,576)		(276,217)
Inventories, net	0		0		0
Deferred Tax Assets, Net, Current	0		0		0
Prepaid Expense and Other Assets, Current	0		0		0
Total current assets	(249,576)		(249,576)		(276,217)
Property, Plant and Equipment, Net	0		0		0
Goodwill	0		0		0
Indefinite-Lived Franchise Rights	0		0		0
Investment in Subsidiaries	(2,102,908)		(2,102,908)		(1,964,442)
Other Assets, Noncurrent	0		0		0
Total assets	(2,352,484)		(2,352,484)		(2,240,659)
Floorplan notes payable - credit facility	0		0		0
Offset account related to floorplan notes payable - credit facility	0		0		0
Floorplan notes payable - manufacturer affiliates	0		0		0
FMCC Offset	0		0		0
Long-term Debt and Capital Lease Obligations, Current	0		0		0
Accounts Payable, Current	0		0		0
Intercompany accounts payable current	(614,248)		(614,248)		(571,638)
Accrued Liabilities, Current	0		0		0
Total current liabilities	(614,248)		(614,248)		(571,638)
LONG-TERM DEBT, net of current maturities	0		0		0
Derivative Liability, Noncurrent	0		0		0
Deferred Income Taxes and Other Liabilities, Noncurrent	0		0		0
Stockholders' Equity Attributable to Parent	(2,102,908)		(2,102,908)		(1,964,442)
Intercompany note receivable	364,672		364,672		295,421
Stockholders' Equity Attributable to Parent Excluding Intercompany Receivables	(1,738,236)		(1,738,236)		(1,669,021)
Total liabilities and stockholders’ equity	$ (2,352,484)		$ (2,352,484)		$ (2,240,659)