Derivative Instruments and Risk Management Activities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Increase Decrease In Floor Plan Interest Expense Due To Interest Rate Hedges	$ 2,800	$ 2,400	$ 8,300	$ 7,300
Derivatives in cash flow hedging relationship
Interest rate swap contracts	(8,199)	577	(12,907)	(5,787)
Location of Loss Reclassified from OCI into Statements of Operations
Floorplan interest expense	$ (9,685)	$ (10,452)	(29,046)	(31,695)
Floorplan Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Floorplan interest expense			(8,306)	(7,331)
Other Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Interest Expense			(1,275)	(1,138)
Interest Rate Swap Contracts [Member]
Derivatives in cash flow hedging relationship
Interest rate swap contracts			$ (12,907)	$ (5,787)