CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Preferred Shares [Member]	Common Shares [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)			(993)			(969)
Issuance of common shares upon conversion of convertible notes	3,149			3,149
Issuance of common shares and deferred compensation amortization, net	6,694			6,694
Dividends/distributions	(40,415)				(39,477)		(938)
Net income	1,814				886		928
Other comprehensive loss	(512)					(512)
Ending Balance at Mar. 31, 2014	1,508,251	94,016	23	2,726,637	(1,339,118)	3,927	22,766
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	652			652
Issuance of common shares and deferred compensation amortization, net	8,815			8,815
Dividends/distributions	(42,183)				(41,383)		(800)
Net income	34,371				33,505		866
Other comprehensive loss	(4,096)					(4,096)
Ending Balance at Mar. 31, 2015	$ 1,506,479	$ 94,016	$ 23	$ 2,772,841	$ (1,379,929)	$ (3,692)	$ 23,220