CONSOLIDATED STATEMENTS OF EQUITY - 6 months ended Jun. 30, 2016 - USD ($) $ in Thousands	Total	Shares of Beneficial Interest, $1.00 Par [Member]	Capital Contributed In Excess Of Par [Member]	Accumulated Other Comprehensive Loss [Member]	Distributions in Excess of Net Income [Member]	Non-controlling interest [Member]	Series B [Member]	Series B [Member] Distributions in Excess of Net Income [Member]	Series A [Member]	Series A [Member] Distributions in Excess of Net Income [Member]	Series A Preferred Shares, $25 plus accrued dividends Liquidation Value [Member]	Series B Preferred Shares, $25 plus accrued dividends Liquidation Value [Member]
Shares Issued Upon Redemption Of Operating Partnership Units		$ 12	$ 250			$ (262)
December 31, 2015 at Dec. 31, 2015	$ 784,630	69,197	1,476,397	$ (4,193)	$ (912,221)	155,369					$ 46	$ 35
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,098					1,190
Net Income (Loss), Excluding Portion Attributable to Noncontrolling Interest					9,908
Other comprehensive loss	(8,326)			(7,436)		(890)
Shares issued under employee compensation plans, net of shares retired	(1,505)	265	(1,770)
Amortization of deferred compensation	2,931		2,931
Distributions paid to common shareholders ($0.42 per share)	(29,170)				(29,170)
Distributions paid to preferred shareholders							$ (3,180)	$ (3,180)	$ (4,744)	$ (4,744)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.42 per unit)	(3,501)					(3,501)
June 30, 2016 at Jun. 30, 2016	$ 748,233	$ 69,474	$ 1,477,808	$ (11,629)	$ (939,407)	$ 151,906					$ 46	$ 35