Net Income Per Common Share (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Basic:
Income from continuing operations available to common stockholders	$ 16,219,000		$ 8,323,000		$ 66,590,000		$ 21,501,000
Income from continuing operations available to common stockholders (in shares)	35,600,772		33,121,728		34,736,311		32,215,549
Income from continuing operations available to common stockholders (in dollars per share)	$ 0.46		$ 0.25		$ 1.92		$ 0.67
Income from discontinued operations	0		(636,000)		9,429,000		4,931,000
Income from discontinued operations (in shares)	35,601,000		33,122,000		34,736,000		32,216,000
Income from discontinued operations (in dollars per share)	$ 0		$ (0.02)		$ 0.27		$ 0.15
Income available to common stockholders	16,219,000		7,687,000		76,019,000		26,432,000
Income available to common stockholders (in dollars per share)	$ 0.46		$ 0.23		$ 2.19		$ 0.82
Effect of Dilutive Securities	0	[1]	0	[1]	0	[1]	0	[1]
Effect of Dilutive Securities (in shares)	99,000	[1]	87,000	[1]	98,000	[1]	89,000	[1]
Diluted:
Income from continuing operations available to common stockholders	16,219,000		8,323,000		66,590,000	[1]	21,501,000	[1]
Adjusted income from continuing operations available to common stockholders ( 1 ) (in shares)	35,700,000		33,209,000		34,834,000	[1]	32,305,000	[1]
Adjusted income from continuing operations available to common stockholders ( 1 ) (in dollars per share)	$ 0.45		$ 0.25		$ 1.91	[1]	$ 0.67	[1]
Adjusted income from discontinued operations available to common stockholders	0		(636,000)		9,429,000		4,931,000
Adjusted income from discontinued operations available to common stockholders (in shares)	35,700,000		33,209,000		34,834,000		32,305,000
Adjusted income from discontinued operations available to common stockholders (in dollars per share)	$ 0		$ (0.02)		$ 0.27		$ 0.15
Total income (Diluted)	16,219,000		7,687,000		76,019,000		26,432,000
Total income per common share amount (in dollars per share)	$ 0.45		$ 0.23		$ 2.18		$ 0.82
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income allocated to convertible limited partnership units	$ 1,100,000		$ 600,000		$ 5,200,000		$ 2,200,000
Convertible Limited Partnership Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted convertible limited partnership units	2,235,783		2,228,404		2,239,987		2,233,088
Anti-dilutive securities (in shares)	2,235,783		2,228,404		2,239,987		2,233,088
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted convertible limited partnership units	18,000		22,000		23,000		29,500
Anti-dilutive securities (in shares)	18,000		22,000		23,000		29,500

[1] Weighted average convertible limited partnership units of 2,235,783 and 2,228,404, which includes vested Series Z incentive units, for the three months ended September 30, 2012, and 2011, respectively, and 2,239,987 and 2,233,088 for the nine months ended September 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 $1.1 million and $0.6 million for the three months ended September 30, 2012 and 2011, respectively, and $5.2 million and $2.2 million for the nine months ended September 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 18,000 and 22,000 for the three months ended September 30, 2012 and 2011, respectively, and stock options of 23,000 and 29,500 for the nine months ended September 30, 2012 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 nine months ended September 30, 2011, as the effect was anti-dilutive.