Consolidated Statements of Beneficiaries' Equity (USD $) In Thousands, except Share data	Total	Series E Preferred Stock [Member]	Common Stock [Member]	Deferred Compensation, Share-based Payments [Member]	Additional Paid-in Capital [Member]	Common Stock In Grantor Trust [Member]	Cumulative Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Distributions [Member]	Noncontrolling Interest [Member]
Beginning Balance at Dec. 31, 2011	$ 1,889,696	$ 43	$ 1,424	$ 5,631	$ 2,776,197	$ (5,631)	$ 477,338	$ (6,079)	$ (1,392,332)	$ 33,105
Beginning Balance, shares at Dec. 31, 2011		4,300,000	142,690,755	292,646
Net income (loss)	9,336						9,202			134
Comprehensive Income (Loss)	75							74		1
Conversion of LP Units to Common Shares, shares			20,464
Conversion of LP Units to Common Shares	(235)				149		(49)			(335)
Bonus Share Issuance, Shares			35,703
Bonus Share Issuance	387				387
Vesting of Restricted Shares, Shares			30,820	9,036
Vesting of Restricted Shares	(89)		1		(90)
Restricted Share Amortization	678				678
Vesting of Restricted Performance Units, Shares			249,797
Vesting of Restricted Performance Units	(1,328)		3		(1,331)
Restricted Performance Units Amortization	479				479
Stock Option Amortization	376				376
Share Issuance from/to Deferred Compensation Plan, Shares			(5,389)	(8,560)
Share Issuance from/to Deferred Compensation Plan	0			(195)		195
Adjustments to Non-controlling Interest	13				303					(290)
Preferred Share distributions	(1,998)								(1,998)
Distributions declared ($0.15 per share)	(21,948)								(21,586)	(362)
Ending Balance at Mar. 31, 2012	1,875,442	43	1,428	5,436	2,777,148	(5,436)	486,491	(6,005)	(1,415,916)	32,253
Ending Balance, shares at Mar. 31, 2012		4,300,000	143,022,150	293,122
Beginning Balance at Dec. 31, 2012	1,773,516	40	1,434	5,352	2,780,194	(5,352)	479,734	(15,918)	(1,493,206)	21,238
Beginning Balance, shares at Dec. 31, 2012		4,000,000	143,538,733	290,745
Net income (loss)	3,919						3,891			28
Comprehensive Income (Loss)	1,893							1,870		23
Equity Issuance Costs	(61)				(61)
Bonus Share Issuance, Shares			27,918
Bonus Share Issuance	361				361
Vesting of Restricted Shares, Shares			21,116	7,050
Vesting of Restricted Shares	(84)				(84)
Restricted Share Amortization	849				849
Vesting of Restricted Performance Units, Shares			26,067
Vesting of Restricted Performance Units	(161)				(161)
Restricted Performance Units Amortization	1,119				1,119
Restricted Share Forfeitures	10						10
Exercise of Stock Options, Shares	76,340		76,340
Exercise of Stock Options	672		1		671
Stock Option Amortization	261				261
Share Issuance from/to Deferred Compensation Plan, Shares			22,404	17,958
Share Issuance from/to Deferred Compensation Plan	0			164		(164)
Adjustments to Non-controlling Interest	0				(19)					19
Preferred Share distributions	(1,725)								(1,725)
Distributions declared ($0.15 per share)	(21,936)								(21,660)	(276)
Ending Balance at Mar. 31, 2013	$ 1,758,633	$ 40	$ 1,435	$ 5,516	$ 2,783,130	$ (5,516)	$ 483,635	$ (14,048)	$ (1,516,591)	$ 21,032
Ending Balance, shares at Mar. 31, 2013		4,000,000	143,712,578	315,753