Derivative Instruments (Details 4) (Cash Flow Hedging, USD $)	0 Months Ended	3 Months Ended		9 Months Ended
	Sep. 17, 2012 item	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Effects of derivative instruments
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)		$ (1,191,000)	$ (1,236,000)	$ 83,000	$ (683,000)
Amount of Loss Reclassified from Accumulated OCI into Income (Effective Portion)		(1,810,000)	(2,631,000)	(6,026,000)	(8,815,000)
Interest expense
Effects of derivative instruments
Amount of Loss Reclassified from Accumulated OCI into Income (Effective Portion)		(1,810,000)	(2,631,000)	(6,026,000)	(8,815,000)
Interest rate contracts
Effects of derivative instruments
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)		(1,191,000)	(1,236,000)	83,000	(683,000)
Number of interest rate swaps terminated	6
Notional value of interest rate swaps terminated	215,000,000
Effective portion of loss on hedge reclassified out of accumulated other comprehensive income and recorded in earnings	$ (10,100,000)