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 Loss [Member]	Cumulative Distributions [Member]	Noncontrolling Interest [Member]
Beginning Balance, Shares at Dec. 31, 2013		4,000,000	156,731,993	312,279
Beginning 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
Net income (loss)	6,942						6,975			(33)
Other comprehensive income (loss)	(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
Net income (loss)	(30,740)						(30,401)			(339)
Other comprehensive income (loss)	$ (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 partnership interest in joint venture	1,025									1,025
Bonus share issuance, Shares			8,447
Bonus share issuance	125				125
Equity issuance costs	(105)				(105)
Share-based compensation activity, Shares			509,675	280,011
Share-based compensation activity	5,097		$ 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
Net income (loss)	40,501						40,191			310
Other comprehensive income (loss)	$ 3,475							3,447		28
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	0
Issuance of partnership interest in consolidated real estate venture	$ 108									108
Conversion of LP Units to Common Shares, Shares			55,303
Conversion of LP Units to Common Shares			$ 1		874					(875)
Share-based compensation activity, Shares			405,200
Share-based compensation activity	5,764		$ 4		5,718		42
Share Issuance from/(to) Deferred Compensation Plan, Shares			(8,311)	153,771
Share issuance from/(to) Deferred Compensation Plan	(47)			$ 1,766	(47)	(1,766)
Adjustment to Non-controlling Interest					(297)					297
Preferred Share distributions	(6,900)								(6,900)
Distributions declared	(111,555)								(110,614)	(941)
Ending Balance, Shares at Dec. 31, 2016		4,000,000	175,140,760	899,457
Ending Balance at Dec. 31, 2016	$ 1,883,437	$ 40	$ 1,752	$ 13,684	$ 3,258,870	$ (13,684)	$ 539,319	$ (1,745)	$ (1,931,892)	$ 17,093