Debt Obligations (Details) (USD $)			12 Months Ended																																							0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Portfolio Term Residual Financing [Member]	Dec. 31, 2011 Bank Term Financings [Member]	Dec. 31, 2012 Deutsche Bank Warehouse Facility [Member]		Dec. 31, 2011 Deutsche Bank Warehouse Facility [Member]		Dec. 31, 2012 Wells Fargo Warehouse Facility [Member]		Dec. 31, 2011 Wells Fargo Warehouse Facility [Member]		Dec. 31, 2012 RBS Warehouse Facility [Member]		Dec. 31, 2011 RBS Warehouse Facility [Member]		Dec. 31, 2011 UBS Warehouse Facility [Member]		Dec. 31, 2012 Revolving Inventory Facility [Member]		Dec. 31, 2011 Revolving Inventory Facility [Member]		Dec. 31, 2012 Real Estate Credit Facility [Member]		Dec. 31, 2012 Equipment Note Payable [Member]		Dec. 31, 2011 Equipment Note Payable [Member]		Dec. 31, 2011 Lender's cost of funds [Member] RBS Warehouse Facility [Member]	Dec. 31, 2012 LIBOR [Member] Bank Term Financings [Member]	Dec. 31, 2012 LIBOR [Member] Deutsche Bank Warehouse Facility [Member]	Dec. 31, 2011 LIBOR [Member] Deutsche Bank Warehouse Facility [Member]	Dec. 31, 2012 LIBOR [Member] Wells Fargo Warehouse Facility [Member]	Dec. 31, 2011 LIBOR [Member] Wells Fargo Warehouse Facility [Member]	Dec. 31, 2012 LIBOR [Member] RBS Warehouse Facility [Member]	Dec. 31, 2012 LIBOR [Member] UBS Warehouse Facility [Member]	Dec. 31, 2012 Prime Rate [Member] Equipment Note Payable [Member]	Dec. 31, 2012 LIBOR [Member] Revolving Inventory Facility [Member]	Dec. 31, 2012 LIBOR [Member] Real Estate Credit Facility [Member]	Dec. 31, 2012 Option One [Member] LIBOR [Member] Portfolio Term Residual Financing [Member]	Dec. 31, 2012 Option Two [Member] LIBOR [Member] Portfolio Term Residual Financing [Member]	Jan. 04, 2013 Subsequent Event [Member] Portfolio Term Residual Financing [Member]	Mar. 31, 2013 Subsequent Event [Member] RBS Warehouse Facility [Member]	Mar. 31, 2013 Subsequent Event [Member] LIBOR [Member] RBS Warehouse Facility [Member]	Dec. 31, 2011 Minimum [Member] Bank Term Financings [Member]	Dec. 31, 2011 Maximum [Member] Bank Term Financings [Member]	Dec. 31, 2012 2012-3 [Member] Securitization Debt [Member]
Debt Instrument [Line Items]
Repurchase Option Percentage	10.00%
Debt Instrument, Interest Rate at Period End			8.62%	8.00%	2.46%	[1]	2.54%	[1]	2.46%	[1]	2.53%	[1]	1.65%	[1],[2]	1.88%	[1]	2.18%	[1]	3.75%	[1]	3.88%	[1]	4.21%	[1]	4.75%	[1]	4.75%	[1]		2.20%
Other Secured Notes Payable	$ 117,281,000	$ 99,296,000																	$ 91,320,000		$ 84,500,000		$ 11,733,000		$ 1,774,000		$ 2,135,000
Debt Instrument, Basis Spread on Variable Rate																													1.50%	2.00%	2.25%	2.25%	2.25%	2.25%	1.40%	1.90%	1.50%	3.50%	4.00%	3.50%	6.00%			2.25%
Debt Instrument, Increase, Additional Borrowings																																										75,000,000
Original Debt Amount																																															$ 350,000,000
Net advance rate					65.00%		58.00%		58.00%		58.00%		53.00%	[2]	53.00%		60.00%		85.00%	[3]	85.00%	[3]	70.00%															85.00%					65.00%		55.90%	67.10%
Contract Service Fee, Percent			7.00%

[1] Interest rate at period end equal to contractual benchmark plus index.

[2] Facility was renewed in March 2013. See Note 16 - Subsequent Events for information on renewal of this facility.

[3] Advance rate is based on qualifying vehicle cost and is secured by our entire inventory.