CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Preferred Shares [Member]	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Distributions in Excess of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-controlling Interests [Member]
Beginning Balance at Dec. 31, 2013	$ 1,539,483	$ 94,016	$ 23	$ 2,717,787	$ (1,300,527)	$ 4,439	$ 23,745
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units	(1,962)			(959)			(1,003)
Issuance of common shares upon conversion of convertible notes	3,149			3,149
Issuance of common shares and deferred compensation amortization, net	15,197			15,197
Dividends/distributions	(82,402)				(80,216)		(2,186)
Net income	17,101				15,336		1,765
Other comprehensive loss	(4,505)					(4,505)
Ending Balance at Jun. 30, 2014	1,486,061	94,016	23	2,735,174	(1,365,407)	(66)	22,321
Beginning Balance at Dec. 31, 2014	1,508,920	94,016	23	2,763,374	(1,372,051)	404	23,154
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares upon conversion of convertible notes	3,733			3,733
Issuance of common shares and deferred compensation amortization, net	17,317			17,316
Dividends/distributions	(84,827)				(82,956)		(1,871)
Net income	84,578				82,837		1,741
Other comprehensive loss	(2,630)					(2,630)
Ending Balance at Jun. 30, 2015	$ 1,527,091	$ 94,016	$ 24	$ 2,784,423	$ (1,372,170)	$ (2,226)	$ 23,024