Fair Value of Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Interest Rate Swap
Recurring Fair Value Measurements:
Effective portion of interest rate contracts	$ (18,237)		$ (18,237)		$ (15,796)
Interest rate swap agreements qualifying as cash flow hedges used for hedging mortgage note payable	175,000		175,000
Derivative, variable rate basis			LIBOR
Decrease (Increase) in fair value of interest rate cash flow hedges	2,404	4,119	2,441	2,074
Recurring | Total Fair value
Recurring Fair Value Measurements:
Effective portion of interest rate contracts	(18,237)		(18,237)
Recurring | Fair Value at Reporting Date Using Significant Other Observable Inputs (Level 2)
Recurring Fair Value Measurements:
Effective portion of interest rate contracts	$ (18,237)		$ (18,237)