CONSOLIDATED STATEMENTS OF EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Shares of Beneficial Interest, $1.00 Par	Capital Contributed in Excess of Par	Accumulated Other Comprehensive Income (Loss)	Distributions in Excess of Net Income	Non- controlling interest	Series B Preferred Stock	Series B Preferred Stock Preferred Shares $.01 par	Series B Preferred Stock Distributions in Excess of Net Income	Series C Preferred Stock	Series C Preferred Stock Preferred Shares $.01 par	Series C Preferred Stock Distributions in Excess of Net Income	Series D Preferred Stock	Series D Preferred Stock Preferred Shares $.01 par	Series D Preferred Stock Distributions in Excess of Net Income
Beginning balance at Dec. 31, 2017	$ 760,991	$ 69,983	$ 1,663,966	$ 7,226	$ (1,109,469)	$ 129,131		$ 35			$ 69			$ 50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(3,712)				(2,601)	(1,111)
Other comprehensive loss	5,103			4,562		541
Shares issued under employee compensation plans, net of shares retired	(195)	370	(565)
Amortization of deferred compensation	1,924		1,924
Dividends paid to common shareholders ($0.21 per share)	(14,766)				(14,766)
Dividends paid to preferred shareholders							$ (1,590)		$ (1,590)	$ (3,105)		$ (3,105)	$ (2,149)		$ (2,149)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(1,737)					(1,737)
Ending balance at Mar. 31, 2018	740,764	70,353	1,665,325	11,788	(1,133,680)	126,824		35			69			50
Beginning balance at Dec. 31, 2017	760,991	69,983	1,663,966	7,226	(1,109,469)	129,131		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(37,669)
Ending balance at Sep. 30, 2018	669,374	70,473	1,669,239	16,505	(1,205,896)	118,899		35			69			50
Beginning balance at Mar. 31, 2018	740,764	70,353	1,665,325	11,788	(1,133,680)	126,824		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(32,321)				(28,202)	(4,119)
Other comprehensive loss	3,193			2,854		339
Shares issued under employee compensation plans, net of shares retired	363	97	266
Amortization of deferred compensation	1,711		1,711
Dividends paid to common shareholders ($0.21 per share)	(14,787)				(14,787)
Dividends paid to preferred shareholders							(1,590)		(1,590)	(3,105)		(3,105)	(2,149)		(2,149)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(1,737)					(1,737)
Ending balance at Jun. 30, 2018	690,342	70,450	1,667,302	14,642	(1,183,513)	121,307		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,636)				(744)	(892)
Other comprehensive loss	2,085			1,863		222
Shares issued under employee compensation plans, net of shares retired	203	23	180
Amortization of deferred compensation	1,757		1,757
Dividends paid to common shareholders ($0.21 per share)	(14,796)				(14,796)
Dividends paid to preferred shareholders							(1,592)		(1,592)	(3,105)		(3,105)	(2,146)		(2,146)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(1,738)					(1,738)
Ending balance at Sep. 30, 2018	669,374	70,473	1,669,239	16,505	(1,205,896)	118,899		35			69			50
Beginning balance at Dec. 31, 2018	546,551	70,495	1,671,042	5,408	(1,306,318)	105,770		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(16,223)				(14,535)	(1,688)
Other comprehensive loss	(6,506)			(5,941)		(565)
Shares issued upon redemption of Operating Partnership units		6,250	89,736			(95,986)
Shares issued under employee compensation plans, net of shares retired	(326)	638	(964)
Amortization of deferred compensation	1,922		1,922
Dividends paid to common shareholders ($0.21 per share)	(14,930)				(14,930)
Dividends paid to preferred shareholders							(1,590)		(1,590)	(3,105)		(3,105)	(2,148)		(2,148)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(1,698)					(1,698)
Ending balance at Mar. 31, 2019	501,947	77,383	1,761,736	(533)	(1,342,626)	5,833		35			69			50
Beginning balance at Dec. 31, 2018	546,551	70,495	1,671,042	5,408	(1,306,318)	105,770		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,413
Ending balance at Sep. 30, 2019	462,490	77,602	1,765,900	(15,388)	(1,370,365)	4,587		35			69			50
Beginning balance at Mar. 31, 2019	501,947	77,383	1,761,736	(533)	(1,342,626)	5,833		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(6,080)				(5,751)	(329)
Other comprehensive loss	(11,647)			(11,342)		(305)
Shares issued under employee compensation plans, net of shares retired	337	164	173
Amortization of deferred compensation	1,889		1,889
Dividends paid to common shareholders ($0.21 per share)	(16,278)				(16,278)
Dividends paid to preferred shareholders							(1,591)		(1,591)	(3,105)		(3,105)	(2,148)		(2,148)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(464)					(464)
Other changes in noncontrolling interest, net	(10)					(10)
Ending balance at Jun. 30, 2019	462,850	77,547	1,763,798	(11,875)	(1,371,499)	4,725		35			69			50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	24,716				24,262	454
Other comprehensive loss	(3,604)			(3,513)		(91)
Shares issued under employee compensation plans, net of shares retired	335	55	280
Amortization of deferred compensation	1,822		1,822
Dividends paid to common shareholders ($0.21 per share)	(16,284)				(16,284)
Dividends paid to preferred shareholders							$ (1,591)		$ (1,591)	$ (3,105)		$ (3,105)	$ (2,148)		$ (2,148)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(425)					(425)
Other changes in noncontrolling interest, net	(76)					(76)
Ending balance at Sep. 30, 2019	$ 462,490	$ 77,602	$ 1,765,900	$ (15,388)	$ (1,370,365)	$ 4,587		$ 35			$ 69			$ 50