Loan Loss Allowance and Credit Quality - Summary of Company's TDRs (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable Modifications [Line Items]
Accrued interest	$ 344,658	$ 319,157
Retail Installment Contracts
Financing Receivable Modifications [Line Items]
Total TDR principal	3,151,614	2,604,351
Accrued interest	85,218	70,965
Discount	(87,743)	(70,321)
Origination costs	4,682	4,161
Outstanding recorded investment	3,153,771	2,609,156
Allowance for loan losses	(551,767)	(475,128)
Outstanding recorded investment, net of allowance	2,602,004	2,134,028
Unsecured Consumer Loans
Financing Receivable Modifications [Line Items]
Total TDR principal	19,540	8,391
Accrued interest	0	0
Discount	(58)	(274)
Origination costs	18	5
Outstanding recorded investment	19,500	8,122
Allowance for loan losses	(6,040)	(2,345)
Outstanding recorded investment, net of allowance	$ 13,460	$ 5,777