Accounting for Derivatives (Details 3) (Derivatives designated as cash flow hedges, Interest rate hedges, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effect of derivative instruments on results of operations
Gain (Loss) Recognized in Other Comprehensive Income (Loss) on Derivatives	$ (5,879)	$ 3,057	$ (5,542)
Interest Expense
Effect of derivative instruments on results of operations
Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss)	$ (4,794)	$ (4,684)	$ (4,761)