Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Numerator:
Income from continuing operations	$ 12,850	[1]	$ 5,402	[1]	$ 14,143	[1]	$ 12,106	[1]	$ 11,153	[1]	$ 8,501	[1]	$ 39,811	[1]	$ 11,445	[1]	$ 44,501		$ 70,910		$ 46,458
Net (income) attributable to noncontrolling interests in the Operating Partnership from continuing operations																	(1,918)		(3,250)		(2,339)
Net (income) attributable to noncontrolling interests in consolidated affiliates from continuing operations	(201)		(249)		(182)		(123)		(204)		148		(215)		(214)		(755)		(485)		(11)
Dividends on Preferred Stock	(627)		(627)		(1,622)		(1,677)		(1,677)		(1,677)		(1,677)		(1,677)		(4,553)		(6,708)		(6,708)
Excess of Preferred Stock redemption/repurchase cost over carrying value	0		0		(1,895)		0										(1,895)		0		0
Income from continuing operations available for common stockholders																	35,380		60,467		37,400
Income from discontinued operations	0	[1]	2,842	[1]	291	[1]	337	[1]	246	[1]	272	[1]	238	[1]	637	[1]	3,470		1,393		15,236
Net (income) attributable to noncontrolling interests in the Operating Partnership from discontinued operations																	(173)		(70)		(858)
Income from discontinued operations available for common stockholders																	3,297		1,323		14,378
Net income available for common stockholders	11,427		7,002		10,112		10,136		9,017		6,878		36,224		9,671		38,677		61,790		51,778
Denominator:
Denominator for basic earnings per Common Share - weighted average shares (in shares)																	72,281,000	[2],[3]	71,578,000	[2],[3]	67,971,000	[2],[3]
Earnings per Common Share - basic:
Income from continuing operations available for common stockholders (in dollars per share)	$ 0.16		$ 0.06		$ 0.14		$ 0.14		$ 0.13		$ 0.10		$ 0.51		$ 0.13		$ 0.49		$ 0.84		$ 0.55
Income from discontinued operations available for common stockholders (in dollars per share)	$ 0.00		$ 0.04		$ 0.00		$ 0.00		$ 0.00		$ 0.00		$ 0.00		$ 0.01		$ 0.05		$ 0.02		$ 0.21
Net income available for common stockholders (in dollars per share)	$ 0.16		$ 0.10		$ 0.14		$ 0.14		$ 0.13		$ 0.10		$ 0.51		$ 0.14		$ 0.54		$ 0.86		$ 0.76
Numerator:
Income from continuing operations	12,850	[1]	5,402	[1]	14,143	[1]	12,106	[1]	11,153	[1]	8,501	[1]	39,811	[1]	11,445	[1]	44,501		70,910		46,458
Net (income) attributable to noncontrolling interests in consolidated affiliates from continuing operations	(201)		(249)		(182)		(123)		(204)		148		(215)		(214)		(755)		(485)		(11)
Dividends on Preferred Stock	(627)		(627)		(1,622)		(1,677)		(1,677)		(1,677)		(1,677)		(1,677)		(4,553)		(6,708)		(6,708)
Excess of Preferred Stock redemption/repurchase cost over carrying value	0		0		(1,895)		0										(1,895)		0		0
Income from continuing operations available for common stockholders before net (income) attributable to noncontrolling interests in the Operating Partnership																	37,298		63,717		39,739
Income from discontinued operations	0	[1]	2,842	[1]	291	[1]	337	[1]	246	[1]	272	[1]	238	[1]	637	[1]	3,470		1,393		15,236
Net income available for common stockholders before net (income) attributable to noncontrolling interests in the Operating Partnership																	$ 40,768		$ 65,110		$ 54,975
Denominator:
Denominator for basic earnings per Common Share - weighted average shares (in shares)																	72,281,000	[2],[3]	71,578,000	[2],[3]	67,971,000	[2],[3]
Stock options using the treasury method																	136,000		198,000		79,000
Noncontrolling interests partnership units																	3,772,000		3,802,000		4,029,000
Denominator for diluted earnings per Common Share - adjusted weighted average shares and assumed conversions (in shares) (1)																	76,189,000	[3]	75,578,000	[3]	72,079,000	[3]
Earnings per Common Share - diluted:
Income from continuing operations available for common stockholders (in dollars per share)	$ 0.16		$ 0.06		$ 0.14		$ 0.14		$ 0.13		$ 0.10		$ 0.50		$ 0.13		$ 0.49		$ 0.84		$ 0.55
Income from discontinued operations available for common stockholders (in dollars per share)	$ 0.00		$ 0.04		$ 0.00		$ 0.00		$ 0.00		$ 0.00		$ 0.00		$ 0.01		$ 0.05		$ 0.02		$ 0.21
Net income available for common stockholders (in dollars per share)	$ 0.16		$ 0.10		$ 0.14		$ 0.14		$ 0.13		$ 0.10		$ 0.50		$ 0.14		$ 0.54		$ 0.86		$ 0.76
Number of anti-dilutive options and warrants not included in earnings per share (in dollars per share)																	400,000		700,000		1,000,000

[1] The amounts presented may not equal to the amounts previously reported in the most recent Form 10-Qs or prior 10-K for each period as a result of discontinued operations.

[2] Includes all unvested restricted stock since dividends on such restricted stock are non-forfeitable.

[3] There were 0.4 million, 0.7 million and 1.0 million options outstanding during the years ended December 31, 2011, 2010 and 2009, respectively, that were not included in the computation of diluted earnings per share because the impact of including such options would be anti-dilutive.