Derivative Financial Instruments (Details 1) (Cash Flow Hedges [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Interest Expense [Member]
Derivatives in fair value and cash flow hedging relationships
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Income	$ (2,683)	$ (752)
Interest rate swaps [Member]
Derivatives in fair value and cash flow hedging relationships
Amount of Gain or (Loss) Recognized in OCI on Derivative	$ (176)	$ (98)