Loan Loss Allowance and Credit Quality - Summary of Activity in Loan Loss Allowance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Retail Installment Contracts Acquired Individually
Allowance for Loan and Lease Losses [Roll Forward]
Balance — beginning of period	$ 2,444,552	$ 1,660,612	$ 2,132,634	$ 1,555,362
Provision for loan losses	527,362	375,281	1,184,068	626,922
Charge-offs	(700,965)	(369,395)	(1,453,530)	(754,121)
Recoveries	397,638	197,815	805,415	436,150
Balance — end of period	2,668,587	1,864,313	2,668,587	1,864,313
Receivables from Dealers Held for Investments
Allowance for Loan and Lease Losses [Roll Forward]
Balance — beginning of period	1,035	0	1,090	0
Provision for loan losses	(112)	1,490	(167)	1,490
Charge-offs	0	0	0
Recoveries	0	0	0	0
Balance — end of period	923	1,490	923	1,490
Unsecured Consumer Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance — beginning of period	203,190	0	179,350	0
Provision for loan losses	70,212	39,256	132,341	39,256
Charge-offs	(66,966)	(6)	(107,914)	(6)
Recoveries	6,518	0	9,177	0
Balance — end of period	$ 212,954	$ 39,250	$ 212,954	$ 39,250