Derivative Instruments and Risk Management Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivatives in cash flow hedging relationship
Interest rate swap contracts	$ (9,856)	$ (11,153)	$ 6,112
Location of Loss Reclassified from OCI into Statements of Operations
Income (Loss) Reclassified from OCI into Statements of Operations	8,313	7,094	6,969
Floorplan Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Income (Loss) Reclassified from OCI into Statements of Operations	(11,486)	(9,837)	(9,938)
Other Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Income (Loss) Reclassified from OCI into Statements of Operations	$ (1,814)	$ (1,513)	$ (1,213)