Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Details) (Inventory of repossessed vehicles, USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory	$ 137,648	$ 129,323
TDRs that have subsequently defaulted (Note 3)	49,502	40,619
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory
TDRs that have subsequently defaulted (Note 3)
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory	137,648	129,323
TDRs that have subsequently defaulted (Note 3)
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory
TDRs that have subsequently defaulted (Note 3)	$ 49,502	$ 40,619