Organization, Basis of Presentation and Significant Accounting Policies (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basic and diluted shares outstanding
Weighted average common shares - basic	129,179,471	95,308,163	124,456,232	95,082,172
Weighted average DownREIT units outstanding (in shares)	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares)	408,428	677,162	415,931	730,531
Weighted average common shares - diluted	129,595,399	95,992,825	124,879,663	95,820,203
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 36,218	$ 156,909	$ 111,648	$ 214,667
Net income allocated to unvested restricted shares	(59)	(547)	(193)	(845)
Net income attributable to common stockholders, adjusted	36,159	156,362	111,455	213,822
Weighted average common shares - basic	129,179,471	95,308,163	124,456,232	95,082,172
Earnings per common share - basic (in dollars per share)	$ 0.28	$ 1.64	$ 0.90	$ 2.25
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	36,218	156,909	111,648	214,667
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	8	7	16	13
Adjusted net income attributable to common stockholders	$ 36,226	$ 156,916	$ 111,664	$ 214,680
Weighted average common shares - diluted	129,595,399	95,992,825	124,879,663	95,820,203
Earnings per common share - diluted (in dollars per share)	$ 0.28	$ 1.63	$ 0.89	$ 2.24
Options to purchase shares of common stock excluded from computation of earnings per share amount			606,318	424,357
Estimated forfeiture rate of stock options (as a percent)			1.20%