Securitization Notes Payable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Rate	Dec. 31, 2011
Debt Instrument, Unamortized Premium	$ 11,150	$ 42,424
Securitized Debt Obligation Liability	9,023,308	6,937,841
Finance Receivables Transferred to Special Purpose Entities	9,902,008
Securitized Debt Obligation Liability - Gross	9,012,158	6,895,417
2006 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Jan. 01, 2014
Secured Debt		63,293
Debt Instrument, Maturity Date Range, End	. NaN, NaN
Original Note Amounts - Minimum	1,200,000
Original Note Amounts - Maximum
Original Weighted-Average Interest Rate - Minimum	5.40%
Original Weighted-Average Interest Rate - Maximum
2007 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Oct. 01, 2013
Secured Debt		793,732
Debt Instrument, Maturity Date Range, End	Mar. 01, 2016
Original Note Amounts - Minimum	1,000,000
Original Note Amounts - Maximum	1,500,000
Original Weighted-Average Interest Rate - Minimum	5.20%
Original Weighted-Average Interest Rate - Maximum	5.50%
2008 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Jan. 01, 2015
Secured Debt	24,126	171,224
Debt Instrument, Maturity Date Range, End	Apr. 01, 2015
Original Note Amounts - Minimum	500,000
Original Weighted-Average Interest Rate - Minimum	8.70%
Original Weighted-Average Interest Rate - Maximum	10.50%
Pledged Assets, Not Separately Reported, Finance Receivables	147,026
2009 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Jan. 01, 2016
Secured Debt	159,832	297,522
Debt Instrument, Maturity Date Range, End	Jul. 01, 2017
Original Note Amounts - Minimum	227,493
Original Note Amounts - Maximum	725,000
Original Weighted-Average Interest Rate - Minimum	2.70%
Original Weighted-Average Interest Rate - Maximum	7.50%
Pledged Assets, Not Separately Reported, Finance Receivables	207,409
2010 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Jul. 01, 2017
Secured Debt	1,095,208	1,756,455
Debt Instrument, Maturity Date Range, End	Apr. 01, 2018
Original Note Amounts - Minimum	200,000
Original Note Amounts - Maximum	850,000
Original Weighted-Average Interest Rate - Minimum	2.20%
Original Weighted-Average Interest Rate - Maximum	3.80%
Pledged Assets, Not Separately Reported, Finance Receivables	1,229,587
2011 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Jul. 01, 2018
Secured Debt	2,518,578	3,813,191
Debt Instrument, Maturity Date Range, End	Mar. 01, 2019
Original Note Amounts - Minimum	800,000
Original Note Amounts - Maximum	1,000,000
Original Weighted-Average Interest Rate - Minimum	2.40%
Original Weighted-Average Interest Rate - Maximum	2.90%
Pledged Assets, Not Separately Reported, Finance Receivables	2,728,474
2012 Transactions [Member]
Debt Instrument, Maturity Date Range, Start	Jun. 01, 2019
Secured Debt	5,214,414
Debt Instrument, Maturity Date Range, End	May 01, 2020
Original Note Amounts - Minimum	800,000
Original Note Amounts - Maximum	1,300,000
Original Weighted-Average Interest Rate - Minimum	1.40%
Original Weighted-Average Interest Rate - Maximum	2.90%
Pledged Assets, Not Separately Reported, Finance Receivables	$ 5,589,512