Derivative Instruments and Risk Management Activities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Floor Plan Interest Expense	$ 10,873	$ 7,863	$ 20,237	$ 15,482
Derivatives in cash flow hedging relationship
Interest rate swap contracts	7,704	(7,122)	7,690	(7,610)
Floorplan Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Floor Plan Interest Expense			(4,848)	(5,344)
Other Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Interest Expense			(606)	(550)
Interest Rate Swap Contracts [Member]
Derivatives in cash flow hedging relationship
Interest rate swap contracts			$ 7,690	$ (7,610)