Consolidated Statements of Beneficiaries' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Deferred Compensation, Share-based Payments [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, 2013		4,000,000	156,731,993		312,280
Beginning Balance at Dec. 31, 2013	$ 1,921,435	$ 40	$ 1,566	$ 2,971,596	$ 5,407	$ (5,407)	$ 522,528	$ (2,995)	$ (1,592,515)	$ 21,215
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(71)						(20)			(51)
Other comprehensive loss	(3,145)							(3,110)		(35)
Equity Issuance Costs	(60)			(60)
Share-based compensation activity, Shares			279,913
Share-based compensation activity	3,629		$ 5	3,612			12
Share Issuance from/to Deferred Compensation Plan, Shares			79,077		74,808
Share issuance from/to Deferred Compensation Plan	(90)			(90)	$ 896	(896)
Adjustments to Non-controlling Interest	0			12						(12)
Preferred Share distributions	(3,450)								(3,450)
Distributions declared	(47,806)								(47,276)	(530)
Ending Balance, Shares at Jun. 30, 2014		4,000,000	157,090,983		387,088
Ending Balance at Jun. 30, 2014	1,870,442	$ 40	$ 1,571	2,975,070	$ 6,303	(6,303)	522,520	(6,105)	(1,643,241)	20,587
Beginning Balance, Shares at Dec. 31, 2014		4,000,000	179,293,160		384,536
Beginning Balance at Dec. 31, 2014	2,159,326	$ 40	$ 1,793	3,314,693	$ 6,219	(6,219)	529,487	(4,607)	(1,700,579)	18,499
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	11,652						11,592			60
Other comprehensive loss	(1,053)							(1,044)		(9)
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	(48)			(48)
Share-based compensation activity, Shares			509,675		280,011
Share-based compensation activity	2,955		$ 6	2,949
Share Issuance from/to Deferred Compensation Plan, Shares			86,839		83,498
Share issuance from/to Deferred Compensation Plan	0				$ 5,777	(5,777)
Adjustments to Non-controlling Interest	0			32						(32)
Preferred Share distributions	(3,450)								(3,450)
Distributions declared	(54,726)								(54,265)	(461)
Ending Balance, Shares at Jun. 30, 2015		4,000,000	179,898,121		748,045
Ending Balance at Jun. 30, 2015	$ 2,115,806	$ 40	$ 1,799	$ 3,317,751	$ 11,996	$ (11,996)	$ 541,079	$ (5,651)	$ (1,758,294)	$ 19,082