Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues and adjusted segment income by reportable segment
Total revenues	$ 2,959,117	$ 2,942,520	$ 2,874,905	$ 2,779,690	$ 2,670,304	$ 2,659,549	$ 2,596,383	$ 2,402,149	$ 11,556,232	$ 10,328,385	$ 9,012,217
Floor plan interest expense									28,515	33,779	34,097
Other interest expense									45,020	49,176	55,085
Debt discount amortization									1,718	8,637	13,043
Depreciation and amortization									48,903	46,253	51,401
Equity in earnings of affiliates									25,451	20,569	13,808
Adjusted segment income (loss)									248,388	187,714	112,811
Retail [Member]
Revenues and adjusted segment income by reportable segment
Total revenues									11,556,232	10,328,385	9,012,217
Floor plan interest expense									28,515	33,779	34,097
Other interest expense									45,020	49,176	55,085
Debt discount amortization									1,718	8,637	13,043
Depreciation and amortization									48,903	46,253	51,401
Equity in earnings of affiliates									2,196	2,577	2,617
Adjusted segment income (loss)									225,133	169,722	101,620
PAG Investments [Member]
Revenues and adjusted segment income by reportable segment
Equity in earnings of affiliates									23,255	17,992	11,191
Adjusted segment income (loss)									$ 23,255	$ 17,992	$ 11,191