Consolidated Statements of Beneficiaries' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Deferred Compensation, Share-based Payments [Member]	Additional Paid-in Capital [Member]	Common Stock In Grantor Trust [Member]	Cumulative Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Distributions [Member]	Noncontrolling Interest [Member]
Beginning Balance, Shares at Dec. 31, 2012		4,000,000	143,538,733	290,745
Beginning Balance at Dec. 31, 2012	$ 1,773,516	$ 40	$ 1,434	$ 5,352	$ 2,780,194	$ (5,352)	$ 479,734	$ (15,918)	$ (1,493,206)	$ 21,238
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	43,189						42,777			412
Other comprehensive income	13,075							12,923		152
Issuance of Common Shares of Beneficial Interest, Shares			12,650,000
Issuance of Common Shares of Beneficial Interest	182,034		$ 127		181,907
Issuance of partnership interest in joint venture	946									946
Equity issuance costs	(744)				(744)
Conversion of LP Units to Common Shares, Shares			81,998
Conversion of LP Units to Common Shares			$ 1		1,239					(1,240)
Bonus share issuance, Shares			27,918
Bonus share issuance	361				361
Share-based compensation activity, Shares			438,356	34,117
Share-based compensation activity	9,438		$ 4		9,417		17
Share Issuance from/to Deferred Compensation Plan, Shares			(5,012)	(12,583)
Share issuance from/to Deferred Compensation Plan				$ 55		(55)
Adjustment to Non-controlling Interest					(778)					778
Preferred Share distributions	(6,900)								(6,900)
Distributions declared	(93,480)								(92,409)	(1,071)
Ending Balance, Shares at Dec. 31, 2013		4,000,000	156,731,993	312,279
Ending Balance at Dec. 31, 2013	1,921,435	$ 40	$ 1,566	$ 5,407	2,971,596	(5,407)	522,528	(2,995)	(1,592,515)	21,215
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	6,942						6,975			(33)
Other comprehensive income	(1,630)							(1,612)		(18)
Issuance of Common Shares of Beneficial Interest, Shares			21,850,000
Issuance of Common Shares of Beneficial Interest	335,398		$ 219		335,179
Equity issuance costs	(495)				(495)
Conversion of LP Units to Common Shares, Shares			228,536
Conversion of LP Units to Common Shares			$ 2		3,612					(3,614)
Share-based compensation activity, Shares			403,902
Share-based compensation activity	6,847		$ 6		6,857		(16)
Share Issuance from/to Deferred Compensation Plan, Shares			80,152	72,257
Share issuance from/to Deferred Compensation Plan	(90)			$ 812	(90)	(812)
Share Choice Plan Issuance, Shares			(1,423)
Adjustment to Non-controlling Interest					(1,966)					1,966
Preferred Share distributions	(6,900)								(6,900)
Distributions declared	(102,181)								(101,164)	(1,017)
Ending Balance, Shares at Dec. 31, 2014		4,000,000	179,293,160	384,536
Ending Balance at Dec. 31, 2014	2,159,326	$ 40	$ 1,793	$ 6,219	3,314,693	(6,219)	529,487	(4,607)	(1,700,579)	18,499
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(30,740)						(30,401)			(339)
Other comprehensive income	$ (590)							(585)		(5)
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	(5,209,437)		(5,209,437)
Repurchase and retirement of Common Shares of Beneficial Interest	$ (67,325)		$ (52)		(67,273)
Issuance of Common Shares of Beneficial Interest	1,025									1,025
Equity issuance costs	(105)				(105)
Bonus share issuance, Shares			8,447
Bonus share issuance	$ 125				125
Share-based compensation activity, Shares	5,097		509,675	280,011
Share-based compensation activity			$ 6		5,091
Share Issuance from/to Deferred Compensation Plan, Shares			88,146	81,139
Share issuance from/to Deferred Compensation Plan	$ (2)			$ 5,699	(2)	(5,699)
Share Choice Plan Issuance, Shares			(1,423)
Adjustment to Non-controlling Interest					93					(93)
Preferred Share distributions	(6,900)								(6,900)
Distributions declared	(107,820)								(106,899)	(921)
Ending Balance, Shares at Dec. 31, 2015		4,000,000	174,688,568	745,686
Ending Balance at Dec. 31, 2015	$ 1,952,091	$ 40	$ 1,747	$ 11,918	$ 3,252,622	$ (11,918)	$ 499,086	$ (5,192)	$ (1,814,378)	$ 18,166