Derivatives and Hedging (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2013 Interest Rate Swap Agreements	Dec. 31, 2012 Interest Rate Swap Agreements	Sep. 30, 2013 Interest Rate Swap Agreements Fair Value, Inputs, Level 2	Dec. 31, 2012 Interest Rate Swap Agreements Fair Value, Inputs, Level 2	Sep. 30, 2013 Interest Rate Swap Agreements Floating Rate Floor Plan Debt	Sep. 30, 2013 Interest Rate Swap Agreements Floating Rate Floor Plan Debt	Sep. 30, 2013 Interest Rate Swap Agreements Floating Rate Floor Plan Debt LIBOR portion	Sep. 30, 2013 Interest Rate Swap Agreements Floating Rate Floor Plan Debt Fixed rate portion	Sep. 30, 2013 Forward foreign exchange contracts Fair Value, Inputs, Level 2
Derivative
Portion of floating rate floor plan debt fixed by swap agreements							$ 300,000	$ 100,000
Interest rate swap, fixed (as a percent)							2.135%	1.55%
Estimated liabilities of swaps designated as hedging instruments, fair value			9,379	14,337
Hedge ineffectiveness recorded	0	0
Increase in the weighted average interest rate on floor plan borrowings due to the swaps (as a percent)					0.35%	0.36%
Estimated asset of contracts designated as hedging instruments, fair value									$ 1,965