Derivative Instruments (Details 4) (Cash Flow Hedging, USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Effects of derivative instruments
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ 438,000	$ 1,071,000	$ 910,000	$ 1,274,000
Amount of Loss Reclassified from Accumulated OCI into Income (Effective Portion)	(393,000)	(1,768,000)	(759,000)	(4,215,000)
Significant ineffectiveness on hedges	0	0	0	0
Interest expense
Effects of derivative instruments
Amount of Loss Reclassified from Accumulated OCI into Income (Effective Portion)	(393,000)	(1,768,000)	(759,000)	(4,215,000)
Interest rate contracts
Effects of derivative instruments
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	438,000	1,071,000	910,000	1,274,000
Amounts of other comprehensive income reclassified to the income statement	$ 500,000	$ 1,800,000	$ 1,000,000	$ 4,300,000