Organization, Basis of Presentation and Significant Accounting Policies (Details 2) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) community Claim home building $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) community Claim home plaintiff building $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares
Basic and diluted shares outstanding
Weighted average common shares - basic (in shares) | shares	136,997,756	133,669,584	136,901,164	132,516,847
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares	499,798	1,032,376	533,642	1,139,423
Weighted average common shares - diluted (in shares) | shares	137,505,054	134,709,460	137,442,306	133,663,770
Calculation of Earnings per Share - basic
Net income attributable to common stockholders | $	$ 356,392	$ 206,142	$ 791,767	$ 586,610
Net income allocated to unvested restricted shares | $	(872)	(467)	(2,036)	(1,444)
Net income attributable to common stockholders, adjusted | $	$ 355,520	$ 205,675	$ 789,731	$ 585,166
Weighted average common shares - basic (in shares) | shares	136,997,756	133,669,584	136,901,164	132,516,847
Earnings per common share - basic (in dollars per share) | $ / shares	$ 2.60	$ 1.54	$ 5.77	$ 4.42
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders | $	$ 356,392	$ 206,142	$ 791,767	$ 586,610
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations | $	10	9	30	28
Adjusted net income available to common stockholders | $	$ 356,402	$ 206,151	$ 791,797	$ 586,638
Weighted average common shares - diluted (in shares) | shares	137,505,054	134,709,460	137,442,306	133,663,770
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 2.59	$ 1.53	$ 5.76	$ 4.39
Estimated forfeiture rate of stock options (as a percent)			0.80%
Loss Contingencies [Line Items]
Number of Real Estate Properties | community	261		261
Number of apartment homes included in operating apartment communities owned | home	75,254		75,254
Avalon at Edgewater [Member]
Loss Contingencies [Line Items]
Number of Real Estate Properties | building	2		2
Number Of Real Estate Properties, Uninhabitable | building	1		1
Number Of Units In Real Estate Property, Uninhabitable | home	240		240
Number of apartment homes included in operating apartment communities owned | home	168		168
Loss Contingency New Class Action Claims Filed Number			3
Loss Contingency Total Class Action Claims Filed Number			4
Loss Contingency, New Claims Filed, Number			20
Loss Contingency, Number of Plaintiffs | plaintiff			141
Loss Contingency, Pending Claims, Number	19		19
Loss Contingency New Subrogation Claims Filed Number			3
Loss Contingency Subrogation Claims Filed Dismissed Number			1
Loss Contingency Subrogation Claims Filed Pending Number			2