Debt - Additional Information (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013
Debt Instrument [Line Items]
Committed amount	$ 15,707,974,000			$ 15,707,974,000			$ 15,273,673,000
Private issuance notes secured with vehicle lease	1,433,658,000			1,433,658,000
Interest expense on secured structured financing	57,217,000		56,626,000	117,079,000		114,336,000
Maturity Year One
Debt Instrument [Line Items]
Debt term				3 years
Credit facility maturity date				Dec. 31, 2016
Maturity Year Two
Debt Instrument [Line Items]
Debt term				5 years
Credit facility maturity date				Dec. 31, 2018
Total Facilities with Santander and Related Subsidiaries
Debt Instrument [Line Items]
Committed amount	4,800,000,000	[1]		4,800,000,000	[1]		4,500,000,000	[2],[3]
Line of Credit Facility Five
Debt Instrument [Line Items]
Committed amount	$ 300,000,000	[1]		$ 300,000,000	[1]

[1] These lines are also collateralized by securitization notes payable and residuals retained by the Company. As of June 30, 2014 and December 31, 2013, $1,569,930 and $1,123,354, respectively, of the aggregate outstanding balances on these facilities were unsecured.

[2] This line is collateralized by residuals retained by the Company.

[3] This line is collateralized by securitization notes payable retained by the Company.