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	16,798				16,107	691
Other Comprehensive Income (Loss), Net of Tax	11,878			11,448		430
Common shares issued in 2013 public offering, net	220,300	11,500	208,800
Shares issued upon redemption of Operating Partnership units		165	2,275			(2,440)
Shares issued under employee compensation plans, net of shares retired	(1,590)	150	(1,740)
Amortization of deferred compensation	4,422		4,422
Distributions paid to common shareholders ($0.36 per share)	(22,402)				(22,402)
Distributions paid to preferred shareholders							(4,744)	(4,744)	(3,180)	(3,180)
Noncontrolling interests:
Distributions paid to Operating Partnership unit holders ($0.36 per unit)	(813)					(813)
Other distributions to noncontrolling interests, net	(266)					(266)
June 30, 2013 at Jun. 30, 2013	$ 933,632	$ 68,146	$ 1,461,487	$ (9,419)	$ (622,853)	$ 36,190					$ 46	$ 35