Loan Loss Allowance and Credit Quality - Summary of Loan Modification Accounted as TDRs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014 contract	Jun. 30, 2013 contract	Jun. 30, 2014 contract	Jun. 30, 2013 contract
Retail Installment Contracts
Financing Receivable Modifications [Line Items]
Outstanding recorded investment before TDR	$ 743,664	$ 473,775	$ 1,367,673	$ 764,636
Outstanding recorded investment after TDR	699,158	444,971	1,280,211	733,812
Number of contracts	44,524	29,797	83,753	50,271
Unsecured Consumer Loans
Financing Receivable Modifications [Line Items]
Outstanding recorded investment before TDR	4,637	150	6,748	150
Outstanding recorded investment after TDR	$ 4,573	$ 149	$ 6,667	$ 149
Number of contracts	4,116	143	6,135	143