Derivative Instruments and Risk Management Activities (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Floor Plan Interest Expense	$ (9,348,000)	$ (10,913,000)
Derivatives in cash flow hedging relationship
Interest rate swap contracts	(6,513,000)	(2,520,000)
Increase Decrease In Floor Plan Interest Expense Due To Interest Rate Hedges	2,700,000	2,400,000
Floorplan Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Floor Plan Interest Expense	(2,708,000)	(2,429,000)
Other Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Interest Expense	(439,000)	(355,000)
Interest Rate Swap Contracts [Member]
Derivatives in cash flow hedging relationship
Interest rate swap contracts	$ (6,513,000)	$ (2,520,000)