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	Jun. 30, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory	$ 140,792	$ 129,323
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	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory	140,792	129,323
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets — repossessed vehicle inventory	$ 0	$ 0