Earnings Per Share and Earnings Per Unit (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Numerator for net income per Unit basic and diluted
Income (loss) from continuing operations	$ 21,195,000	$ (9,945,000)	$ 16,495,000	$ (29,153,000)
Allocation to Noncontrolling Interests - Operating Partnership, net	814,000	(628,000)	(457,000)	1,725,000
Net (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(71,000)	185,000	(31,000)	435,000
Preferred distributions	(3,467,000)	(3,618,000)	(6,933,000)	(7,238,000)
Income (loss) from continuing operations available to Common Shares, net of Noncontrolling Interests	16,843,000	(12,750,000)	9,074,000	(34,231,000)
Discontinued operations, net of Noncontrolling Interests	535,614,000	19,093,000	667,248,000	92,437,000
Net income available to Common Shares	552,457,000	6,343,000	676,322,000	58,206,000
Numerator for net income per share - diluted:
Income (loss) from continuing operations	21,195,000	(9,945,000)	16,495,000	(29,153,000)
Net (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(71,000)	185,000	(31,000)	435,000
Preferred distributions	(3,467,000)	(3,618,000)	(6,933,000)	(7,238,000)
Income from continuing operations available to common shares	17,657,000		9,531,000
Discontinued operations, net	560,558,000	20,034,000	698,324,000	97,098,000
Numerator for net income per share - diluted	578,215,000	6,343,000	707,855,000	58,206,000
Denominator for net income per share - basic and diluted:
Denominator for net income per share - basic	294,663,000	282,217,000	293,784,000	281,435,000
Effect of dilutive securities:
OP Units	13,291,000		13,322,000
Long-term compensation award shares/units	4,245,000		4,274,000
Denominator for net income per share - diluted	312,199,000	282,217,000	311,380,000	281,435,000
Net income per share - basic	$ 1.875	$ 0.022	$ 2.302	$ 0.207
Net income per share - diluted	$ 1.852	$ 0.022	$ 2.273	$ 0.207
Net income per share - basic:
Income (loss) from continuing operations available to Common Shares, net of Noncontrolling Interests	$ 0.057	$ (0.045)	$ 0.031	$ (0.121)
Discontinued operations, net of Noncontrolling Interests	$ 1.818	$ 0.067	$ 2.271	$ 0.328
Net income per share - basic	$ 1.875	$ 0.022	$ 2.302	$ 0.207
Net income per share - diluted:
Income (loss) from continuing operations available to Common Shares	$ 0.057	$ (0.045)	$ 0.031	$ (0.121)
Discontinued operations, net	$ 1.795	$ 0.067	$ 2.242	$ 0.328
Net income per share - diluted	$ 1.852	$ 0.022	$ 2.273	$ 0.207
Earnings Per Share (Textuals) [Abstract]
Convertible preferred shares	0	397,004	0	397,306
Unsecured Notes, face amount	650,000,000		650,000,000
Convertible Notes, outstanding	$ 482,500,000		$ 482,500,000