Organization, Basis of Presentation and Significant Accounting Policies (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic and diluted shares outstanding
Weighted average common shares - basic	131,330,078	129,208,839	130,165,873	126,057,793
Weighted average DownREIT units outstanding (in shares)	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares)	568,417	0	554,627	411,821
Weighted average common shares - diluted	131,905,995	129,216,339	130,728,000	126,477,114
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 241,100	$ (10,715)	$ 540,929	$ 100,929
Net income allocated to unvested restricted shares	(366)	16	(858)	(166)
Net income attributable to common stockholders, adjusted	240,734	(10,699)	540,071	100,763
Weighted average common shares - basic	131,330,078	129,208,839	130,165,873	126,057,793
Earnings per common share - basic (in dollars per share)	$ 1.83	$ (0.08)	$ 4.15	$ 0.80
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	241,100	(10,715)	540,929	100,929
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	9	8	26	24
Adjusted net income available to common stockholders	$ 241,109	$ (10,707)	$ 540,955	$ 100,953
Weighted average common shares - diluted	131,905,995	129,216,339	130,728,000	126,477,114
Earnings per common share - diluted (in dollars per share)	$ 1.83	$ (0.08)	$ 4.14	$ 0.80
Options to purchase shares of common stock excluded from computation of earnings per share amount (in shares)			1,499	605,899
Estimated forfeiture rate of stock options (as a percent)			1.40%