Related-Party Transactions - Additional Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			3 Months Ended	12 Months Ended			3 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Dealer Loan Portfolio	Dec. 31, 2013 Dealer Loan Portfolio	Mar. 31, 2014 Serviced Auto Loan And Retail Installment	Dec. 31, 2013 Serviced Auto Loan And Retail Installment	Mar. 31, 2014 SHUSA	Mar. 31, 2014 SBNA	Mar. 31, 2014 SBNA Serviced Auto Loan And Retail Installment	Mar. 31, 2013 SBNA Serviced Auto Loan And Retail Installment	Mar. 31, 2014 Produban Servicios Informaticos Generales S.L	Mar. 31, 2013 Produban Servicios Informaticos Generales S.L
Class Of Stock [Line Items]
Interest expense on line of credit	$ 24,874	$ 6,494						$ 363
Accrued interest expense on line of credit	10,119		11,435					213
Letter of credit fees	125	144
Accrued fees on letter of credit	125		128
Notional	12,580,549		10,461,378
Derivative instrument interest expenses	8,881	4,874
Receivables sold					222,384
Servicing fee income on receivables sold				1,265
Servicing fees receivables				464					3,685
Servicing fees receivable				997	817	(661)	3,163		94	865	6,214
Expenses incurred												22	38
Reimbursed expenses	$ 0	$ 381