Unaudited Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total gross revenues	$ 107,954	[1]	$ 106,708	[1]	$ 105,571	[1]	$ 104,139	[1]	$ 100,458	[1]	$ 87,895	[1]	$ 88,398	[1]	$ 85,159	[1]	$ 424,372	$ 361,910	$ 297,008
Net income (loss)	38,185		42,177		15,287		1,814		(7,001)		5,155		7,832		(2,123)		97,463	3,863	184,638
Net income (loss) attributable to common shareholders	$ 35,700		$ 38,720		$ 12,743		$ (839)		$ (8,923)		$ 2,978		$ (849)		$ (7,295)		$ 93,104	$ 1,630	$ 180,316
Net income (loss) attributable to common shareholders - basic per share	$ 0.15		$ 0.17		$ 0.05		$ 0.00		$ (0.04)		$ 0.01		$ 0.00		$ (0.04)		$ 0.38	$ (0.07)	$ 0.99
Net income (loss) attributable to common shareholders - diluted per share	$ 0.15		$ 0.17		$ 0.05		$ 0.00		$ (0.04)		$ 0.01		$ 0.00		$ (0.04)		$ 0.38	$ (0.07)	$ 0.93

[1] All periods have been adjusted to reflect the impact of properties sold during the years ended December 31, 2014 and 2013, and properties classified as held for sale, which are reflected in discontinued operations in the Consolidated Statements of Operations.