Organization, Basis of Presentation and Significant Accounting Policies (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Basic and diluted shares outstanding
Weighted average common shares - basic	129,288,771	119,680,510
Weighted average DownREIT units outstanding (in shares)	7,500	7,500
Effect of dilutive securities (in shares)	333,286	423,118
Weighted average common shares - diluted	129,629,557	120,111,128
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 141,739	$ 75,427
Net income allocated to unvested restricted shares	(232)	(139)
Net income attributable to common stockholders, adjusted	141,507	75,288
Weighted average common shares - basic	129,288,771	119,680,510
Earnings per common share - basic (in dollars per share)	$ 1.09	$ 0.63
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	141,739	75,427
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	9	8
Adjusted net income available to common stockholders	$ 141,748	$ 75,435
Weighted average common shares - diluted	129,629,557	120,111,128
Earnings per common share - diluted (in dollars per share)	$ 1.09	$ 0.63
Options to purchase shares of common stock excluded from computation of earnings per share amount (in shares)	605,899	608,148
Estimated forfeiture rate of stock options (as a percent)	1.00%