Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues and adjusted segment income by reportable segment
Total revenues	$ 3,371,252	$ 3,329,854	$ 3,306,021	$ 3,156,390	$ 2,858,467	$ 2,832,517	$ 2,767,068	$ 2,669,440	$ 13,163,517	$ 11,127,492	$ 9,943,350
Floor plan interest expense									38,797	27,218	32,822
Other interest expense									46,892	44,256	48,541
Debt discount amortization										1,718	8,637
Depreciation									53,995	47,101	44,523
Equity in earnings of affiliates									27,572	25,451	20,569
Adjusted segment Income									288,988	247,857	185,636
Reconciliation of total adjusted segment income to consolidated income from continuing operations before income taxes
Adjusted segment Income									288,988	247,857	185,636
Debt redemption costs									(17,753)
Gain on debt repurchase											1,634
Income from continuing operations before income taxes									288,988	247,857	185,636
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	5,378,990				4,499,401				5,378,990	4,499,401
Equity method investments	303,160				298,640				303,160	298,640
Capital expenditures									161,286	131,971	74,900
Reportable Segments
Revenues and adjusted segment income by reportable segment
Total revenues									13,163,517	11,127,492	9,943,350
Floor plan interest expense									38,797	27,218	32,822
Other interest expense									46,892	44,256	48,541
Debt discount amortization										1,718	8,637
Depreciation									53,995	47,101	44,523
Equity in earnings of affiliates									27,572	25,451	20,569
Adjusted segment Income									306,741	247,857	184,002
Reconciliation of total adjusted segment income to consolidated income from continuing operations before income taxes
Adjusted segment Income									306,741	247,857	184,002
Income from continuing operations before income taxes									306,741	247,857	184,002
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	5,378,990				4,499,401				5,378,990	4,499,401
Equity method investments	303,160				298,640				303,160	298,640
Capital expenditures									161,286	131,971	74,900
Retail
Revenues and adjusted segment income by reportable segment
Total revenues									13,164,070	11,127,492	9,943,350
Floor plan interest expense									38,797	27,218	32,822
Other interest expense									46,782	44,256	48,541
Debt discount amortization										1,718	8,637
Depreciation									53,980	47,101	44,523
Equity in earnings of affiliates									3,238	2,196	2,577
Adjusted segment Income									283,094	224,602	166,010
Reconciliation of total adjusted segment income to consolidated income from continuing operations before income taxes
Adjusted segment Income									283,094	224,602	166,010
Income from continuing operations before income taxes									283,094	224,602	166,010
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	5,101,289				4,250,672				5,101,289	4,250,672
Equity method investments	53,288				49,911				53,288	49,911
Capital expenditures									151,411	131,971	74,900
Other
Revenues and adjusted segment income by reportable segment
Total revenues									4,030
Other interest expense									110
Depreciation									15
Equity in earnings of affiliates									24,334	23,255	17,992
Adjusted segment Income									23,713	23,255	17,992
Reconciliation of total adjusted segment income to consolidated income from continuing operations before income taxes
Adjusted segment Income									23,713	23,255	17,992
Income from continuing operations before income taxes									23,713	23,255	17,992
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	277,767				248,729				277,767	248,729
Equity method investments	249,872				248,729				249,872	248,729
Capital expenditures									9,875
Unallocated amount to segment
Reconciliation of total adjusted segment income to consolidated income from continuing operations before income taxes
Debt redemption costs									(17,753)
Gain on debt repurchase											1,634
Intersegment Elimination
Revenues and adjusted segment income by reportable segment
Total revenues									(4,583)
Adjusted segment Income									(66)
Reconciliation of total adjusted segment income to consolidated income from continuing operations before income taxes
Adjusted segment Income									(66)
Income from continuing operations before income taxes									(66)
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	$ (66)								$ (66)