CONSOLIDATED STATEMENTS OF EQUITY - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Shares of Beneficial Interest, $1.00 Par [Member]	Capital Contributed In Excess Of Par [Member]	AOCI Attributable to Parent [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 C Preferred Stock [Member]	Series D Preferred Stock [Member]
December 31, 2017 at Dec. 31, 2017	$ 760,991	$ 69,983	$ 1,663,966	$ 7,226	$ (1,117,290)	$ 136,952	$ 35		$ 69	$ 50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(3,712)					(394)
Net Income (Loss), Excluding Portion Attributable to Noncontrolling Interest					(3,318)
Other comprehensive income	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
Distributions paid to common shareholders ($0.21 per share)	(14,766)				(14,766)
Distributions paid to preferred shareholders							(1,590)	$ (1,590)	(3,105)	(2,149)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.21 per unit)	(1,737)					(1,737)
March 31, 2018 at Mar. 31, 2018	$ 740,764	$ 70,353	$ 1,665,325	$ 11,788	$ (1,142,218)	$ 135,362	$ 35		$ 69	$ 50