Loan Loss Allowance and Credit Quality - Summary of Delinquencies (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable Recorded Investment Past Due [Line Items]
Principal, current	$ 22,028,789	$ 20,111,640
Principal, 31-60 days past due	2,023,330	2,050,688
Delinquent principal over 60 days	896,577	1,037,013
Total principal	24,948,696	23,199,341
Loans Acquired Individually
Financing Receivable Recorded Investment Past Due [Line Items]
Principal, current	21,047,173	18,653,827
Principal, 31-60 days past due	1,829,261	1,729,139
Delinquent principal over 60 days	799,455	855,315
Total principal	23,675,889	21,238,281
Purchased Receivables Portfolios
Financing Receivable Recorded Investment Past Due [Line Items]
Principal, current	981,616	1,457,813
Principal, 31-60 days past due	194,069	321,549
Delinquent principal over 60 days	97,122	181,698
Total principal	1,272,807	1,961,060
Receivables from Dealers Held for Investments
Financing Receivable Recorded Investment Past Due [Line Items]
Principal, current	85,885	95,835
Principal, 31-60 days past due	0	0
Delinquent principal over 60 days	0	0
Total principal	85,885	95,835
Unsecured Consumer Loans
Financing Receivable Recorded Investment Past Due [Line Items]
Principal, current	1,283,884	1,072,316
Principal, 31-60 days past due	45,382	28,102
Delinquent principal over 60 days	119,443	65,360
Total principal	$ 1,448,709	$ 1,165,778