Earnings Per Share and Earnings Per Unit (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Aug. 18, 2011
Numerator for net income per Unit basic and diluted
Income (loss) from continuing operations	$ 35,491,000	$ (295,000)	$ 47,908,000	$ (32,667,000)
Allocation to Noncontrolling Interests - Operating Partnership, net	1,371,000	(173,000)	(1,648,000)	2,042,000
Partially Owned Properties	(387,000)	188,000	(418,000)	623,000
Preferred distributions	(3,466,000)	(3,617,000)	(10,399,000)	(10,855,000)
Income (loss) from continuing operations available to Common Shares, net of Noncontrolling Interests	30,267,000	(3,551,000)	35,443,000	(40,857,000)
Discontinued operations, net of Noncontrolling Interests	74,115,000	28,717,000	745,261,000	124,229,000
Net income available to Common Shares	104,382,000	25,166,000	780,704,000	83,372,000
Numerator for net income per share - diluted:
Income (loss) from continuing operations	35,491,000	(295,000)	47,908,000	(32,667,000)
Partially Owned Properties	(387,000)	188,000	(418,000)	623,000
Preferred distributions	(3,466,000)	(3,617,000)	(10,399,000)	(10,855,000)
Income from continuing operations available to common shares	31,638,000		37,091,000
Discontinued operations, net	77,486,000	30,121,000	779,888,000	130,438,000
Numerator for net income per share - diluted	109,124,000	25,166,000	816,979,000	83,372,000
Denominator for net income per share - basic and diluted:
Denominator for net income per share - basic	295,831,000	282,717,000	294,474,000	281,867,000
Effect of dilutive securities:
OP Units	13,053,000		13,231,000
Long-term compensation award shares/units	3,960,000		4,203,000
Denominator for net income per share - diluted	312,844,000	282,717,000	311,908,000	281,867,000
Net income per share - basic	$ 0.35	$ 0.09	$ 2.65	$ 0.30
Net income per share - diluted	$ 0.35	$ 0.09	$ 2.62	$ 0.30
Net income per share - basic:
Income (loss) from continuing operations available to Common Shares, net of Noncontrolling Interests	$ 0.102	$ (0.013)	$ 0.12	$ (0.145)
Discontinued operations, net of Noncontrolling Interests	$ 0.251	$ 0.102	$ 2.531	$ 0.441
Net income per share - basic	$ 0.35	$ 0.09	$ 2.65	$ 0.30
Net income per share - diluted:
Income (loss) from continuing operations available to Common Shares	$ 0.10	$ (0.01)	$ 0.12	$ (0.15)
Discontinued operations, net	$ 0.248	$ 0.102	$ 2.500	$ 0.441
Net income per share - diluted	$ 0.35	$ 0.09	$ 2.62	$ 0.30
Earnings Per Share (Textuals) [Abstract]
Convertible preferred shares	0	393,724	0	396,098
Unsecured Notes, face amount	650,000,000		650,000,000
Convertible Notes, outstanding	$ 482,500,000		$ 482,500,000		$ 482,500,000