Organization, Basis of Presentation and Significant Accounting Policies (Details 2) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) community home building $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) community Claim home plaintiff building $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares
Basic and diluted shares outstanding
Weighted average common shares - basic (in shares) | shares	137,715,192	136,997,756	137,457,293	136,901,164
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares	584,354	499,798	541,399	533,642
Weighted average common shares - diluted (in shares) | shares	138,307,046	137,505,054	138,006,192	137,442,306
Calculation of Earnings per Share - basic
Net income attributable to common stockholders | $	$ 238,248	$ 356,392	$ 639,348	$ 791,767
Net income allocated to unvested restricted shares | $	(672)	(872)	(1,794)	(2,036)
Net income attributable to common stockholders, adjusted | $	$ 237,576	$ 355,520	$ 637,554	$ 789,731
Weighted average common shares - basic (in shares) | shares	137,715,192	136,997,756	137,457,293	136,901,164
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.73	$ 2.60	$ 4.64	$ 5.77
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders | $	$ 238,248	$ 356,392	$ 639,348	$ 791,767
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships | $	11	10	32	30
Adjusted net income attributable to common stockholders | $	$ 238,259	$ 356,402	$ 639,380	$ 791,797
Weighted average common shares - diluted (in shares) | shares	138,307,046	137,505,054	138,006,192	137,442,306
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.72	$ 2.59	$ 4.63	$ 5.76
Loss Contingencies [Line Items]
Number of operating apartment communities | community	263		263
Number of apartment homes included in operating apartment communities owned | home	76,076		76,076
Avalon at Edgewater
Loss Contingencies [Line Items]
Number of operating apartment communities | building	2		2
Number of operating apartment communities, uninhabitable | building	1		1
Number of units in operating apartment communities, 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 class action claims filed, number of apartments included in settlement			66
Loss Contingency Class Action Claims Filed, Number of Apartments Included in Settlement Submitted			42
Loss Contingency Class Action Claims Filed, Number of Apartments Included in Settlement Submitted Amount | $			$ 6,800
Loss contingency, total class action claims filed number			4
Loss contingency, new claims filed, number			19
Loss contingency, number of plaintiffs | plaintiff			143
Loss contingency, claims filed, number, not consolidated			1
Loss contingency, number of plaintiffs, remaining in class action settlement | plaintiff			2
Loss contingency, claims filed, number, consolidated			18
Loss contingency, new subrogation claims filed, number			6
Loss contingency, subrogation claims filed dismissed, number			1
Loss Contingency Subrogation Claims Filed Pending Not Dismissed Number			1
Loss contingency, subrogation claims filed pending, number			4