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, 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
Beginning Balance at Dec. 31, 2015	1,462,531	94,016	23	2,776,837	(1,428,908)	(1,939)	22,502
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common shares	(8,973)			(8,973)
Issuance of common shares and deferred compensation amortization, net	5,925		1	5,924
Dividends/distributions	(42,104)				(41,415)		(689)
Net income	50,792				49,769		1,023
Other comprehensive loss	(4,625)					(4,625)
Ending Balance at Mar. 31, 2016	$ 1,463,546	$ 94,016	$ 24	$ 2,773,788	$ (1,420,554)	$ (6,564)	$ 22,836