Debt Obligations Portfolio Term Financing (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Line of Credit Facility [Line Items]
Portfolio Term Financings	$ 989,206	$ 1,049,478
Securitization Debt [Member]
Line of Credit Facility [Line Items]
Portfolio Term Financings	569,884	677,118
Pooled Auto Loan Program Financings [Member]
Line of Credit Facility [Line Items]
Portfolio Term Financings	319,322	347,360
Portfolio Term Residual Financing [Member]
Line of Credit Facility [Line Items]
Portfolio Term Financings	$ 100,000	$ 25,000