Unaudited Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Total gross revenues	$ 109,606	[1]	$ 96,950	[1]	$ 97,763	[1]	$ 94,121	[1]	$ 92,059	[1]	$ 83,800	[1]	$ 78,961	[1]	$ 75,360	[1]	$ 398,440	$ 330,180	$ 292,298
Net income (loss)	(7,001)		5,155		7,832		(2,123)		(1,755)		175,289		5,626		5,478		3,863	184,638	(89,778)
Net income (loss) attributable to common shareholders	$ (8,923)		$ 2,978		$ (849)		$ (7,295)		$ (7,039)		$ 168,943		$ (3,392)		$ (2,187)		$ 1,630	$ 180,316	$ (79,584)
Net income (loss) attributable to common shareholders - basic per share	$ (0.04)		$ 0.01		$ 0		$ (0.04)		$ (0.04)		$ 1.09		$ (0.02)		$ (0.01)		$ (0.07)	$ 0.99	$ (0.68)
Net income (loss) attributable to common shareholders - diluted per share	$ (0.04)		$ 0.01		$ 0		$ (0.04)		$ (0.04)		$ 0.96		$ (0.02)		$ (0.01)		$ (0.07)	$ 0.93	$ (0.68)

[1] All periods have been adjusted to reflect the impact of properties sold during the years ended December 31, 2013 and 2012, and properties classified as held for sale, which are reflected in discontinued operations in the Consolidated Statements of Operations.