Organization, Basis of Presentation and Significant Accounting Policies (Details 2) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) community Claim home plaintiff building $ / shares shares	Mar. 31, 2016 USD ($) $ / shares shares
Basic and diluted shares outstanding
Weighted average common shares - basic (in shares) | shares	137,068,874	136,785,880
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500
Effect of dilutive securities (in shares) | shares	454,868	589,664
Weighted average common shares - diluted (in shares) | shares	137,531,242	137,383,044
Calculation of Earnings per Share - basic
Net income attributable to common stockholders | $	$ 235,875	$ 237,931
Net income allocated to unvested restricted shares | $	(652)	(632)
Net income attributable to common stockholders, adjusted | $	$ 235,223	$ 237,299
Weighted average common shares - basic (in shares) | shares	137,068,874	136,785,880
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.72	$ 1.73
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders | $	$ 235,875	$ 237,931
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships | $	11	10
Adjusted net income attributable to common stockholders | $	$ 235,886	$ 237,941
Weighted average common shares - diluted (in shares) | shares	137,531,242	137,383,044
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.72	$ 1.73
Loss Contingencies [Line Items]
Number of operating apartment communities | community	260
Number of apartment homes included in operating apartment communities owned | home	74,952
Avalon at Edgewater [Member]
Loss Contingencies [Line Items]
Total number of class action lawsuits	5
Number of operating apartment communities | building	2
Number of operating apartment communities, uninhabitable | building	1
Number of units in operating apartment communities, uninhabitable | home	240
Number of apartment homes included in operating apartment communities owned | home	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	19
Loss contingency, number of plaintiffs | plaintiff	146
Loss contingency, new subrogation claims filed, number	5
Loss contingency, subrogation claims filed dismissed, number	1
Loss contingency, subrogation claims filed pending, number	4