Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Numerator:
Income from continuing operations	$ 14,143		$ 39,811		$ 26,249		$ 51,256
Net (income) attributable to noncontrolling interests in the Operating Partnership from continuing operations	(608)		(1,921)		(1,098)		(2,409)
Net (income) attributable to noncontrolling interests in consolidated affiliates from continuing operations	(182)		(215)		(305)		(429)
Dividends on Preferred Stock	(1,622)		(1,677)		(3,299)		(3,354)
Excess of Preferred Stock redemption/repurchase cost over carrying value	(1,895)		0		(1,895)		0
Income from continuing operations available for common stockholders	9,836		35,998		19,652		45,064
Income from discontinued operations	291		238		628		875
Net (income) attributable to noncontrolling interests in the Operating Partnership from discontinued operations	(15)		(12)		(32)		(44)
Income from discontinued operations available for common stockholders	276		226		596		831
Net income available for common stockholders	10,112		36,224		20,248		45,895
Denominator:
Denominator for basic earnings per Common Share - weighted average shares	72,211,000		71,601,000		72,015,000		71,508,000
Earnings per Common Share - basic:
Income from continuing operations available for common stockholders (in dollars per share)	$ 0.14		$ 0.51		$ 0.27		$ 0.63
Income from discontinued operations available for common stockholders (in dollars per share)	$ 0.00		$ 0.00		$ 0.01		$ 0.01
Net income available for common stockholders (in dollars per share)	$ 0.14		$ 0.51		$ 0.28		$ 0.64
Numerator:
Income from continuing operations	14,143		39,811		26,249		51,256
Net (income) attributable to noncontrolling interests in consolidated affiliates from continuing operations	(182)		(215)		(305)		(429)
Dividends on Preferred Stock	(1,622)		(1,677)		(3,299)		(3,354)
Excess of Preferred Stock redemption/repurchase cost over carrying value	(1,895)		0		(1,895)		0
Income from continuing operations available for common stockholders before net (income) attributable to noncontrolling interests in the Operating Partnership	10,444		37,919		20,750		47,473
Income from discontinued operations available for common stockholders	291		238		628		875
Net income available for common stockholders before net (income) attributable to noncontrolling interests in the Operating Partnership	$ 10,735		$ 38,157		$ 21,378		$ 48,348
Denominator:
Denominator for basic earnings per Common Share -weighted average shares	72,211,000		71,601,000		72,015,000		71,508,000
Stock options using the treasury method	202,000		209,000		185,000		188,000
Noncontrolling interests partnership units	3,784,000		3,797,000		3,787,000		3,808,000
Denominator for diluted earnings per Common Share - adjusted weighted average shares and assumed conversions (1)	76,197,000	[1]	75,607,000	[1]	75,987,000	[1]	75,504,000	[1]
Earnings per Common Share - diluted:
Income from continuing operations available for common stockholders (in dollars per share)	$ 0.14		$ 0.50		$ 0.27		$ 0.63
Income from discontinued operations available for common stockholders (in dollars per share)	$ 0.00		$ 0.00		$ 0.01		$ 0.01
Net income available for common stockholders (in dollars per share)	$ 0.14		$ 0.50		$ 0.28		$ 0.64
Number of anti-dilutive options and warrants not included in earnings per share (in dollars per share)	300,000		300,000		600,000		600,000

[1] There were 0.3 million and 0.6 million options outstanding during the three and six months ended June 30, 2011 and 2010, respectively, that were not included in the computation of diluted earnings per share because the impact of including such options would be anti-dilutive.