CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, unless otherwise specified	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 A [Member]	Series A [Member] Distributions in Excess of Net Income [Member]	Series B [Member]	Series B [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, 2012 at Dec. 31, 2012	$ 713,229	$ 56,331	$ 1,247,730	$ (20,867)	$ (608,634)	$ 38,588					$ 46	$ 35
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,382				28,309	1,073
Comprehensive income	13,513			13,063		450
Common shares issued in 2013 public offering, net	220,300	11,500	208,800
Shares issued upon redemption of Operating Partnership units		172	2,371			(2,543)
Shares issued under employee compensation plans, net of shares retired	(1,103)	199	(1,302)
Amortization of deferred compensation	6,246		6,246
Distributions paid to common shareholders ($0.54 per share)	(34,674)				(34,674)
Distributions paid to preferred shareholders							(7,115)	(7,115)	(4,771)	(4,771)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.54 per unit)	(1,198)					(1,198)
Amortization of historic tax credit	(1,810)					(1,810)
Other distributions to noncontrolling interests, net	(272)					(272)
September 30, 2013 at Sep. 30, 2013	$ 931,727	$ 68,202	$ 1,463,845	$ (7,804)	$ (626,885)	$ 34,288					$ 46	$ 35