Organization, Basis of Presentation and Significant Accounting Policies (Details 2) $ / shares in Units, $ in Thousands	3 Months Ended		15 Months Ended
	Mar. 31, 2016 USD ($) community Claim home plaintiff building $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) community home building
Loss Contingencies [Line Items]
Impairment of Real Estate	$ (2,202)	$ 5,788
Number of Real Estate Properties | community	258		258
Number of apartment homes included in operating apartment communities owned | home	75,379		75,379
Basic and diluted shares outstanding
Weighted average common shares - basic | shares	136,785,880	131,883,741
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500
Effect of dilutive securities (in shares) | shares	589,664	1,284,532
Weighted average common shares - diluted | shares	137,383,044	133,175,773
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 237,931	$ 208,144
Net income allocated to unvested restricted shares	(632)	(529)
Net income attributable to common stockholders, adjusted	$ 237,299	$ 207,615
Weighted average common shares - basic | shares	136,785,880	131,883,741
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.73	$ 1.57
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	$ 237,931	$ 208,144
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	10	9
Adjusted net income available to common stockholders	$ 237,941	$ 208,153
Weighted average common shares - diluted | shares	137,383,044	133,175,773
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.73	$ 1.56
Estimated forfeiture rate of stock options (as a percent)	0.80%
Avalon at Edgewater [Member]
Loss Contingencies [Line Items]
Impairment of Real Estate	$ (8,702)	$ 793
Gain on Business Interruption Insurance Recovery	$ 20,306
Number of Real Estate Properties | building	2		2
Number of apartment homes included in operating apartment communities owned | home	168		168
Loss Contingency New Class Action Claims Filed Number | Claim	4
Loss Contingency, New Claims Filed, Number | Claim	19
Loss Contingency, Number of Plaintiffs | plaintiff	138
Insurance Proceeds	$ 29,008	$ 22,142	$ 73,008
Number Of Real Estate Properties, Uninhabitable | building	1		1
Number Of Units In Real Estate Property, Uninhabitable | home	240		240