CONSOLIDATED STATEMENTS OF EQUITY - 3 months ended Mar. 31, 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]
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	1,929					208
Net Income (Loss), Excluding Portion Attributable to Noncontrolling Interest					1,721
Other comprehensive loss	(5,446)			(4,859)		(587)
Shares issued under employee compensation plans, net of shares retired	(1,716)	262	(1,978)
Amortization of deferred compensation	1,573		1,573
Distributions paid to common shareholders ($0.21 per share)	(14,584)				(14,584)
Distributions paid to preferred shareholders							$ (1,590)	$ (1,590)	$ (2,372)	$ (2,372)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(1,752)					(1,752)
March 31, 2016 at Mar. 31, 2016	$ 760,672	$ 69,459	$ 1,475,992	$ (9,052)	$ (929,046)	$ 153,238					$ 46	$ 35