CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Thousands, $ in Thousands	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]
Preferred Stock, Dividends, Per Share, Cash Paid							$ 1.8438		$ 2.0625
Beginning Balance at Dec. 31, 2012	$ 713,229	$ 56,331	$ 1,247,730	$ (20,867)	$ (608,634)	$ 38,588	$ 35		$ 46
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,213				35,859	1,354
Other comprehensive income	14,716			14,230		486
Shares issued upon redemption of Operating Partnership units	0
Shares issued under employee and trustee compensation plans, net of shares retired	566	290	276
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)
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 income	(14,262)				(13,830)	(432)
Other comprehensive income	654			635		19
Shares issued upon redemption of Operating Partnership units	0	(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)		$ (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
Preferred Stock, Dividends, Per Share, Cash Paid							$ 1.8438		$ 2.0625
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(129,567)				(116,683)	(12,884)
Other comprehensive income	2,027			1,809		218
Shares issued upon redemption of Operating Partnership units		(34)	(675)			(709)
Shares issued under employee and trustee compensation plans, net of shares retired	(4,383)	362	(4,745)
Amortization of deferred compensation	6,284		6,284
Distributions paid to common shareholders	(58,085)				(58,085)
Distributions paid to preferred shareholders	(15,848)						$ (6,361)	$ (6,361)	$ (9,487)	$ (9,487)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders	(5,703)					(5,703)
Contributions from noncontrolling interest, net	(20)					(20)
Ending Balance at Dec. 31, 2015	$ 784,630	$ 69,197	$ 1,476,397	$ (4,193)	$ (912,221)	$ 155,369	$ 35		$ 46
Noncontrolling interests:
Other Ownership Interests, Units Issued	145,188					145,188