Consolidated Statements of Beneficiaries' Equity (USD $) In Thousands, except Share data	Total	Total Preferred Shares	Series C Preferred Stock [Member]	Series E Preferred Stock [Member]	Common Stock	Treasury Stock	Deferred Compensation Payable in Common Shares	Common Shares in Grantor Trust	Additional Paid-in Capital	Cumulative Earnings	Accumulated Other Comprehensive Income (Loss)	Cumulative Distributions	Non-Controlling Interests
Beginning Balance at Dec. 31, 2010	$ 1,977,774	$ 43			$ 1,343	$ (3,074)	$ 5,774	$ (5,774)	$ 2,671,217	$ 483,439	$ (1,945)	$ (1,301,521)	$ 128,272
Beginning Balance, shares at Dec. 31, 2010		4,300,000			134,601,796	116,679	291,281
Net income (loss)	(113)									(259)			146
Comprehensive income (loss)	(487)										(479)		(8)
Issuance of Common Shares of Beneficial Interest	8,272				7				8,265
Issuance of Common Shares of Beneficial Interest, shares					679,285
Equity issuance costs	338								(308)				30
Conversion of LP Units to Common Shares	0				1				1,098				(1,099)
Conversion of LP Units to Common Shares, shares					92,992
Bonus Share Issuance	6					12	6	(6)		(6)
Bonus Share Issuance, shares						(463)	463
Vesting of Restricted Shares	(352)				1	3,062			(1,818)	(1,597)
Vesting of Restricted Shares, shares					85,248	(116,216)	9,043
Restricted Share Amortization	2,228								2,228
Restricted Performance Units Amortization	1,229								1,229
Exercise of Stock Options	659				1				658
Exercise of Stock Options, shares					120,179
Share Option Amortization	1,105								1,105
Outperformance Plan Amortization	128								128
Outperformance Plan Amortization, shares
Share Issuance from/to Deferred Compensation Plan	(16)						(149)	149	(16)
Share Issuance from/to Deferred Compensation Plan, shares					(845)		(8,141)
Share Choice Plan Issuance Shares					(1,684)
Share Choice Plan Issuance	(55)								(55)
Stock Issued During Period, Value, Other	32								32
Stock Issued During Period, Shares, Other					2,672
Adjustment to Non-controlling Interest	0								3,037				(3,037)
Preferred Share distributions	(5,994)											(5,994)
Preferred share redemption charge	0
Distributions declared ($0.45), and ($0.45) per share in September 30, 2012 and September 30, 2011, respectively	(63,184)											(61,294)	(1,890)
Ending Balance at Sep. 30, 2011	1,920,894	43			1,353	0	5,631	(5,631)	2,686,800	481,577	(2,424)	(1,368,809)	122,354
Ending Balance, shares at Sep. 30, 2011		4,300,000			135,579,643	0	292,646
Beginning Balance at Dec. 31, 2011		43				0				477,338			33,105
Beginning Balance, shares at Dec. 31, 2011		4,300,000				0
Net income (loss)										32,804			423
Ending Balance at Jun. 30, 2012
Beginning Balance at Dec. 31, 2011	1,889,696	43			1,424	0	5,631	(5,631)	2,776,197	477,338	(6,079)	(1,392,332)	33,105
Beginning Balance, shares at Dec. 31, 2011		4,300,000			142,690,755	0	292,646
Net income (loss)	33,227
Comprehensive income (loss)	(14,580)										(14,377)		(203)
Preferred Stock, Shares Issued		2,300,000	0	4,000,000
Preferred Stock, Value, Issued	96,850	23	0	40
Preferred Stock, Including Additional Paid in Capital, Net of Discount									96,810
Equity issuance costs	(610)								(610)
Stock Redeemed or Called During Period, Shares			(2,000,000)
Additional Paid in Capital, Preferred Stock									(47,890)
Stock Redeemed or Called During Period, Value	(47,910)		(20)
Conversion of LP Units to Common Shares	(231)				1				149	(49)			(332)
Conversion of LP Units to Common Shares, shares					20,464
Bonus Share Issuance	387								387
Bonus Share Issuance, shares					35,703
Vesting of Restricted Shares	(1,291)				3				(1,294)
Vesting of Restricted Shares, shares					280,851		9,036
Restricted Share Amortization	2,138								2,138
Vesting of Restricted Performance Units	(1,329)				2				(1,331)
Vesting of Restricted Performance Units, shares					249,797
Restricted Performance Units Amortization	1,926								1,926
Exercise of Stock Options	748				2				746
Exercise of Stock Options, shares	165,159				165,159
Share Option Amortization	1,121								1,121
Share Issuance from/to Deferred Compensation Plan	0						(279)	279
Share Issuance from/to Deferred Compensation Plan, shares					(5,564)		10,937
Stock Issued During Period, Value, Other	15								15
Stock Issued During Period, Shares, Other					1,336
Adjustment to Non-controlling Interest	11								358				(347)
Preferred Share distributions	(7,832)											(7,832)
Preferred share redemption charge	(2,090)											(2,090)
Distributions declared ($0.45), and ($0.45) per share in September 30, 2012 and September 30, 2011, respectively	(66,037)											(64,804)	(1,233)
Ending Balance at Sep. 30, 2012	1,884,209	63			1,432	0	5,352	(5,352)	2,828,722	510,093	(20,456)	(1,467,058)	31,413
Ending Balance, shares at Sep. 30, 2012		6,300,000			143,438,501	0	290,745
Beginning Balance at Jun. 30, 2012
Net income (loss)	17,089
Comprehensive income (loss)	(4,081)
Preferred Stock, Shares Issued		2,300,000		4,000,000
Preferred Stock, Value, Issued	96,850	23		40
Preferred share redemption charge	0
Ending Balance at Sep. 30, 2012	$ 1,884,209	$ 63				$ 0
Ending Balance, shares at Sep. 30, 2012		6,300,000				0