Net Income Per Common Share (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Basic:
Income from operations available to common stockholders	$ 5,337,000		$ 9,329,000		$ 13,589,000	[1]	$ 22,320,000	[1]
Income from operations available to common stockholders: weighted average common shares (in shares)	32,040,904		29,329,273		31,754,949		29,149,562
Income from operations available to common stockholders: per share amount (in dollars per share)	$ 0.17		$ 0.32		$ 0.43	[1]	$ 0.77	[1]
Income from discontinued operations available to common stockholders	4,988,000		153,000		5,154,000		289,000
Income from discontinued operations available to common stockholders: weighted average common shares (in shares)	32,041		29,329		31,755		29,150
Income from discontinued operations available to common stockholders: per share amount (in dollars per share)	$ 0.15		$ 0		$ 0.16		$ 0.01
Total income	10,325,000		9,482,000		18,743,000		22,609,000
Effect of Dilutive Securities: Income	0	[1],[2]	0	[1],[2]	0	[1],[2]	0	[1],[2]
Effect of Dilutive Securities: weighted average common shares (in shares)	94	[1],[2]	73	[1],[2]	89	[1],[2]	64	[1],[2]
Effect of Dilutive Securities: per share amount (in dollars per share)	0		0		0		0
Total income per common share amount (in dollars per share)	$ 0.32		$ 0.32		$ 0.59		$ 0.78
Diluted:
Income from operations available to common stockholders	5,337,000		9,329,000		13,589,000	[1]	22,320,000	[1]
Income from operations available to common stockholders: weighted average common shares (in shares)	32,135,064		29,402,635		31,844,002		29,213,613
Income from operations available to common stockholders: per share amount (in dollars per share)	$ 0.17		$ 0.32		$ 0.43	[1]	$ 0.76	[1]
Income from discontinued operations available to common stockholders	4,988,000		153,000		5,154,000		289,000
Income from discontinued operations available to common stockholders: weighted average common shares (in shares)	32,135		29,402		31,844	[1]	29,214	[1]
Income from discontinued operations available to common stockholders: per share amount (in dollars per share)	$ 0.15		$ 0		$ 0.16		$ 0.01
Total income (diluted)	10,325,000		9,482,000		18,743,000		22,609,000
Total income per common share amount (in dollars per share)	$ 0.32		$ 0.32		$ 0.59		$ 0.77
Convertible Limited Partnership Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	2,230,354		2,357,321		2,235,468		2,388,406
Net income allocated to convertible limited partnership units	$ 1,000,000		$ 800,000		$ 1,600,000		$ 1,900,000
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	29,500		131,664		41,250		147,690

[1] Net income allocated to convertible limited partnership units, which includes vested Series Z units, aggregating $1.0 million and $0.8 million for the three months ended June 30, 2011 and 2010 respectively, and $1.6 million and $1.9 million for the six months ended June 30, 2011 and 2010, respectively, have been excluded from income available to common stock holders for the calculation of net 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.

[2] Weighted average convertible limited partnership units of 2,230,354 and 2,235,468, which includes vested Series Z incentive units, for the three and six months ended June 30, 2011 and weighted convertible limited partnership units of 2,357,321 and 2,388,406 which includes vested Series Z incentive units, for the three and six months ended June 30, 2010, respectively, were not included in the determination of diluted EPS because they were 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.