Net Income Per Common Share (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Basic:
Income from continuing operations available to common stockholders	$ 37,078,000		$ 5,135,000		$ 49,932,000		$ 13,183,000
Income from continuing operations available to common stockholders (in shares)	34,570,772		32,040,904		34,299,331		31,754,949
Income from continuing operations available to common stockholders (in dollars per share)	$ 1.07		$ 0.16		$ 1.47		$ 0.41
Income from discontinued operations	0		5,190,000		9,868,000		5,560,000
Income from discontinued operations (in shares)	34,571,000		32,041,000		34,299,000		31,755,000
Income from discontinued operations (in dollars per share)	$ 0		$ 0.16		$ 0.27		$ 0.18
Income available to common stockholders	37,078,000		10,325,000		59,800,000		18,743,000
Income available to common stockholders (in dollars per share)	$ 1.07		$ 0.32		$ 1.74		$ 0.59
Effect of Dilutive Securities	54,000	[1]	0	[1]	108,000	[1]	0	[1]
Effect of Dilutive Securities (in shares)	137,000	[1]	94,000	[1]	132,000	[1]	89,000	[1]
Diluted:
Income from continuing operations available to common stockholders	37,132,000		5,135,000		50,040,000	[1]	13,183,000	[1]
Adjusted income from continuing operations available to common stockholders ( 1 ) (in shares)	34,708,000		32,135,000		34,431,000	[1]	31,844,000	[1]
Adjusted income from continuing operations available to common stockholders ( 1 ) (in dollars per share)	$ 1.07		$ 0.16		$ 1.47	[1]	$ 0.41	[1]
Adjusted income from discontinued operations available to common stockholders	0		5,190,000		9,868,000		5,560,000
Adjusted income from discontinued operations available to common stockholders (in shares)	34,708,000		32,135,000		34,431,000		31,844,000
Adjusted income from discontinued operations available to common stockholders (in dollars per share)	$ 0		$ 0.16		$ 0.27		$ 0.18
Total income (Diluted)	37,132,000		10,325,000		59,908,000		18,743,000
Total income per common share amount (in dollars per share)	$ 1.07		$ 0.32		$ 1.74		$ 0.59
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income allocated to convertible limited partnership units	$ 2,500,000		$ 1,000,000		$ 3,500,000		$ 1,600,000
Convertible Limited Partnership Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted convertible limited partnership units	2,239,057		2,230,354		2,242,112		2,230,354
Anti-dilutive securities (in shares)	2,239,057		2,230,354		2,242,112		2,230,354
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted convertible limited partnership units			29,500				41,250
Anti-dilutive securities (in shares)			29,500				41,250

[1] Weighted average convertible limited partnership units of 2,239,057 and 2,230,354, which includes vested Series Z incentive units, for the three months ended June 30, 2012, and 2011, respectively, and 2,242,112 and 2,230,354 for the six months ended June 30, 2012 and 2011, respectively, were not included in the determination of diluted EPS because they were anti-dilutive. Income allocated to convertible limited partnership units, which includes vested Series Z units, aggregating $2.5 million and $1.0 million for the three months ended June 30, 2012 and 2011, respectively, and $3.5 million and $1.6 million for the six months ended June 30, 2012 and 2011, respectively, have been excluded from income available to common stock holders for the calculation of diluted income per common share since these units are excluded from the diluted weighted average common shares for the period as the effect was anti-dilutive. The Company has the ability to redeem DownREIT limited partnership units for cash and does not consider them to be potentially dilutive securities. Stock options of 29,500 and 41,250 for the three and six months ended June 30, and 2011, respectively, were not included in the diluted earnings per share calculation because the effects on earnings per share were anti-dilutive. All shares of Series G cumulative convertible preferred stock have been excluded in diluted earnings per share for the three and six months ended June 30, 2011, as the effect was anti-dilutive.