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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic and diluted shares outstanding
Weighted average common shares - basic	129,856,335	129,179,471	129,574,118	124,456,232
Weighted average DownREIT units outstanding (in shares)	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares)	384,486	408,428	356,614	415,931
Weighted average common shares - diluted	130,248,321	129,595,399	129,938,232	124,879,663
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 158,086	$ 36,218	$ 299,825	$ 111,648
Net income allocated to unvested restricted shares	(254)	(59)	(487)	(193)
Net income attributable to common stockholders, adjusted	157,832	36,159	299,338	111,455
Weighted average common shares - basic	129,856,335	129,179,471	129,574,118	124,456,232
Earnings per common share - basic (in dollars per share)	$ 1.22	$ 0.28	$ 2.31	$ 0.90
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	158,086	36,218	299,825	111,648
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	9	8	17	16
Adjusted net income available to common stockholders	$ 158,095	$ 36,226	$ 299,842	$ 111,664
Weighted average common shares - diluted	130,248,321	129,595,399	129,938,232	124,879,663
Earnings per common share - diluted (in dollars per share)	$ 1.21	$ 0.28	$ 2.31	$ 0.89
Options to purchase shares of common stock excluded from computation of earnings per share amount (in shares)			243,326	606,318
Estimated forfeiture rate of stock options (as a percent)			1.10%