Segment Information (Reconciliation of Consolidated Net Operating Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Reportable_Segments	Mar. 31, 2013
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Consolidated net operating income	$ 90,140	$ 84,485
Less:
Interest expense	(31,844)	(30,914)
Interest expense — amortization of deferred financing costs	(1,189)	(1,161)
Interest expense — financing obligation	(272)	(218)
Depreciation and amortization	(52,570)	(49,476)
General and administrative expenses	(8,181)	(6,551)
Net Gain (Loss) On Real Estate Venture Transactions, including real estate venture formation	(135)	0
Loss on early extinguishment of debt	0	(3)
Plus:
Interest income	385	58
Equity in income of real estate ventures	242	1,535
Net gain (loss) on sale of undepreciated real estate	1,187	0
Loss from continuing operations	(2,237)	(2,245)
Income (Loss) from Discontinued Operations	(8)	6,164
Net income	$ (2,245)	$ 3,919
Number of Reportable Segments	7