Condensed Consolidated Financial Information Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 13,037	$ 40,975	$ 20,215	$ 4,650
Contracts-in-transit and vehicle receivables, net	252,438	237,448
Accounts and notes receivable, net	157,768	151,330
Intercompany accounts receivable	0	0
Inventory, Net	1,737,751	1,556,705
Deferred income taxes	14,109	11,062
Prepaid expenses and other current assets	27,852	37,699
Total current assets	2,202,955	2,035,219
PROPERTY AND EQUIPMENT, net	1,033,981	950,388
GOODWILL	854,915	830,377	737,303
INTANGIBLE FRANCHISE RIGHTS	307,588	303,947
INVESTMENT IN SUBSIDIARIES	0	0
OTHER ASSETS	15,490	21,561
Total assets	4,414,929	4,141,492
Floorplan notes payable - credit facility and other	1,265,719	1,143,246
Offset account related to floorplan notes payable - credit facility	(110,759)	(39,616)
Floorplan notes payable - manufacturer affiliates	389,071	307,656
FMCC Offset	(25,500)	(22,500)
Current maturities of long-term debt and short-term financing	55,193	72,630
Accounts payable	280,423	288,320
Intercompany accounts payable	0	0
Accrued expenses	185,323	172,463
Total current liabilities	2,039,470	1,922,199
LONG-TERM DEBT, net of current maturities	1,203,436	1,008,837
LIABILITIES FROM INTEREST RATE RISK MANAGEMENT ACTIVITIES	31,153	25,311
DEFERRED INCOME TAXES AND OTHER LIABILITIES	222,618	207,135
Group 1 stockholders’ equity	918,252	978,010	1,035,175	860,284
Intercompany note receivable	0	0
Total stockholders’ equity	918,252	978,010
Total liabilities and stockholders' equity	4,414,929	4,141,492
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	0	0	0	0
Contracts-in-transit and vehicle receivables, net	0	0
Accounts and notes receivable, net	0	0
Intercompany accounts receivable	0	0
Inventory, Net	0	0
Deferred income taxes	264	196
Prepaid expenses and other current assets	5,586	590
Total current assets	5,850	786
PROPERTY AND EQUIPMENT, net	0	0
GOODWILL	0	0
INTANGIBLE FRANCHISE RIGHTS	0	0
INVESTMENT IN SUBSIDIARIES	2,388,081	1,964,442
OTHER ASSETS	0	0
Total assets	2,393,931	1,965,228
Floorplan notes payable - credit facility and other	0	0
Offset account related to floorplan notes payable - credit facility	0	0
Floorplan notes payable - manufacturer affiliates	0	0
FMCC Offset	0	0
Current maturities of long-term debt and short-term financing	0	0
Accounts payable	0	0
Intercompany accounts payable	500,171	295,421
Accrued expenses	0	0
Total current liabilities	500,171	295,421
LONG-TERM DEBT, net of current maturities	837,526	609,812
LIABILITIES FROM INTEREST RATE RISK MANAGEMENT ACTIVITIES	0	0
DEFERRED INCOME TAXES AND OTHER LIABILITIES	(1)	0
Group 1 stockholders’ equity	1,056,235	1,059,995
Intercompany note receivable	0	0
Total stockholders’ equity	1,056,235	1,059,995
Total liabilities and stockholders' equity	2,393,931	1,965,228
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	6,338	25,379	4,306	4,341
Contracts-in-transit and vehicle receivables, net	233,275	218,361
Accounts and notes receivable, net	132,078	117,427
Intercompany accounts receivable	1,192	276,217
Inventory, Net	1,533,166	1,342,022
Deferred income taxes	13,845	10,866
Prepaid expenses and other current assets	9,117	22,039
Total current assets	1,929,011	2,012,311
PROPERTY AND EQUIPMENT, net	916,338	839,063
GOODWILL	809,775	700,642
INTANGIBLE FRANCHISE RIGHTS	285,659	257,502
INVESTMENT IN SUBSIDIARIES	0	0
OTHER ASSETS	9,321	10,120
Total assets	3,950,104	3,819,638
Floorplan notes payable - credit facility and other	1,261,606	1,137,743
Offset account related to floorplan notes payable - credit facility	(110,759)	(39,616)
Floorplan notes payable - manufacturer affiliates	303,810	207,329
FMCC Offset	(25,500)	(22,500)
Current maturities of long-term debt and short-term financing	47,186	61,185
Accounts payable	178,544	176,143
Intercompany accounts payable	0	0
Accrued expenses	167,509	149,700
Total current liabilities	1,822,396	1,669,984
LONG-TERM DEBT, net of current maturities	300,997	347,202
LIABILITIES FROM INTEREST RATE RISK MANAGEMENT ACTIVITIES	31,153	25,311
DEFERRED INCOME TAXES AND OTHER LIABILITIES	217,669	193,077
Group 1 stockholders’ equity	2,078,060	1,879,485
Intercompany note receivable	(500,171)	(295,421)
Total stockholders’ equity	1,577,889	1,584,064
Total liabilities and stockholders' equity	3,950,104	3,819,638
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	6,699	15,596	$ 15,909	$ 309
Contracts-in-transit and vehicle receivables, net	19,163	19,087
Accounts and notes receivable, net	25,690	33,903
Intercompany accounts receivable	0	0
Inventory, Net	204,585	214,683
Deferred income taxes	0	0
Prepaid expenses and other current assets	13,149	15,070
Total current assets	269,286	298,339
PROPERTY AND EQUIPMENT, net	117,643	111,325
GOODWILL	45,140	129,735
INTANGIBLE FRANCHISE RIGHTS	21,929	46,445
INVESTMENT IN SUBSIDIARIES	0	0
OTHER ASSETS	6,169	11,441
Total assets	460,167	597,285
Floorplan notes payable - credit facility and other	4,113	5,503
Offset account related to floorplan notes payable - credit facility	0	0
Floorplan notes payable - manufacturer affiliates	85,261	100,327
FMCC Offset	0	0
Current maturities of long-term debt and short-term financing	8,007	11,445
Accounts payable	101,879	112,177
Intercompany accounts payable	1,192	276,217
Accrued expenses	17,814	22,763
Total current liabilities	218,266	528,432
LONG-TERM DEBT, net of current maturities	64,913	51,823
LIABILITIES FROM INTEREST RATE RISK MANAGEMENT ACTIVITIES	0	0
DEFERRED INCOME TAXES AND OTHER LIABILITIES	4,950	14,058
Group 1 stockholders’ equity	172,038	2,972
Intercompany note receivable	0	0
Total stockholders’ equity	172,038	2,972
Total liabilities and stockholders' equity	460,167	597,285
Consolidation, Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	0	0
Contracts-in-transit and vehicle receivables, net	0	0
Accounts and notes receivable, net	0	0
Intercompany accounts receivable	(1,192)	(276,217)
Inventory, Net	0	0
Deferred income taxes	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(1,192)	(276,217)
PROPERTY AND EQUIPMENT, net	0	0
GOODWILL	0	0
INTANGIBLE FRANCHISE RIGHTS	0	0
INVESTMENT IN SUBSIDIARIES	(2,388,081)	(1,964,442)
OTHER ASSETS	0	0
Total assets	(2,389,273)	(2,240,659)
Floorplan notes payable - credit facility and other	0	0
Offset account related to floorplan notes payable - credit facility	0	0
Floorplan notes payable - manufacturer affiliates	0	0
FMCC Offset	0	0
Current maturities of long-term debt and short-term financing	0	0
Accounts payable	0	0
Intercompany accounts payable	(501,363)	(571,638)
Accrued expenses	0	0
Total current liabilities	(501,363)	(571,638)
LONG-TERM DEBT, net of current maturities	0	0
LIABILITIES FROM INTEREST RATE RISK MANAGEMENT ACTIVITIES	0	0
DEFERRED INCOME TAXES AND OTHER LIABILITIES	0	0
Group 1 stockholders’ equity	(2,388,081)	(1,964,442)
Intercompany note receivable	500,171	295,421
Total stockholders’ equity	(1,887,910)	(1,669,021)
Total liabilities and stockholders' equity	$ (2,389,273)	$ (2,240,659)