CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, except Per Share data, unless otherwise specified	Total		Shares of Beneficial Interest, $1.00 Par [Member]	Capital Contributed in Excess of Par [Member]	Accumulated Other Comprehensive (Income) Loss [Member]	Distributions in Excess of Net Income [Member]	Non- controlling interest [Member]	Series B Preferred Stock [Member]	Series B Preferred Stock [Member] Distributions in Excess of Net Income [Member]	Series A Preferred Stock [Member]	Series A Preferred Stock [Member] Distributions in Excess of Net Income [Member]
Beginning Balance at Dec. 31, 2011	$ 588,038		$ 55,677	$ 1,047,487	$ (34,099)	$ (524,738)	$ 43,711
Preferred Stock, Dividends, Per Share, Cash Paid								$ 0.3278		$ 1.3464
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(42,550)					(40,837)	(1,713)
Other comprehensive income	13,789				13,232		557
Shares issued upon redemption of Operating Partnership units	0		28	413			(441)
Shares issued under employee and trustee compensation plans, net of shares retired	(4,722)		626	(5,348)
Share offering	194,231			194,150				35		46
Amortization of deferred compensation	11,028			11,028
Distributions paid to common shareholders	(35,735)					(35,735)
Distributions paid to preferred shareholders	(7,984)							(1,131)		(6,193)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders	(1,459)						(1,459)
Amortization of historic tax credit	(1,810)						(1,810)
Contributions from noncontrolling interest, net	(257)						(257)
Ending Balance at Dec. 31, 2012	713,229		56,331	1,247,730	(20,867)	(608,634)	38,588
Preferred Stock, Dividends, Per Share, Cash Paid								$ 1.8438		$ 2.0625
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	37,213	[1]				35,859	1,354
Other comprehensive income	14,716				14,230		486
Shares issued upon redemption of Operating Partnership units	0		172	2,372			(2,544)
Shares issued under employee and trustee compensation plans, net of shares retired	566		290	276
Share offering	220,511		11,500	209,011
Amortization of deferred compensation	8,071			8,071
Distributions paid to common shareholders	(48,315)					(48,315)
Distributions paid to preferred shareholders	(15,848)							(6,361)		(9,488)	(9,488)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders	(1,626)						(1,626)
Amortization of historic tax credit	(1,810)						(1,810)
Contributions from noncontrolling interest, net	(254)						(254)
Ending Balance at Dec. 31, 2013	926,452		68,293	1,467,460	(6,637)	(636,939)	34,194	35		46
Preferred Stock, Dividends, Per Share, Cash Paid								$ 1.8438		$ 2.0625
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(14,262)	[1]				(13,830)	(432)
Other comprehensive income	654				635		19
Shares issued upon redemption of Operating Partnership units			7	131			(138)
Shares issued under employee and trustee compensation plans, net of shares retired	(1,362)		501	(1,863)
Amortization of deferred compensation	8,455			8,455
Distributions paid to common shareholders	(54,988)					(54,988)
Distributions paid to preferred shareholders	(15,848)							(6,361)	(6,361)	(9,487)	(9,487)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders	(1,703)						(1,703)
Amortization of historic tax credit	(581)						(581)
Contributions from noncontrolling interest, net	(2,080)						(2,080)
Ending Balance at Dec. 31, 2014	$ 844,737		$ 68,801	$ 1,474,183	$ (6,002)	$ (721,605)	$ 29,279	$ 35		$ 46

[1] Includes gains on sales of discontinued operations (before non controlling interest) of $33.4 million (1st Quarter 2013), $45.1 million (3rd Quarter 2013).