Organization, Basis of Presentation and Significant Accounting Policies (Details 2) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) community home building $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) community Claim home building $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares
Basic and diluted shares outstanding
Weighted average common shares - basic (in shares) | shares	137,848,788	137,715,192	137,818,076	137,457,293
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares	466,776	584,354	405,148	541,399
Weighted average common shares - diluted (in shares) | shares	138,323,064	138,307,046	138,230,724	138,006,192
Calculation of Earnings per Share - basic
Net income attributable to common stockholders | $	$ 192,486	$ 238,248	$ 588,791	$ 639,348
Net income allocated to unvested restricted shares | $	(555)	(672)	(1,722)	(1,794)
Net income attributable to common stockholders, adjusted | $	$ 191,931	$ 237,576	$ 587,069	$ 637,554
Weighted average common shares - basic (in shares) | shares	137,848,788	137,715,192	137,818,076	137,457,293
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.39	$ 1.73	$ 4.26	$ 4.64
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders | $	$ 192,486	$ 238,248	$ 588,791	$ 639,348
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships | $	11	11	33	32
Adjusted net income attributable to common stockholders | $	$ 192,497	$ 238,259	$ 588,824	$ 639,380
Weighted average common shares - diluted (in shares) | shares	138,323,064	138,307,046	138,230,724	138,006,192
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.39	$ 1.72	$ 4.26	$ 4.63
Loss Contingencies [Line Items]
Number of operating apartment communities | community	271		271
Number of apartment homes included in operating apartment communities owned | home	78,383		78,383
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 | Claim			3
Loss contingency class action claims filed, number of apartments included in settlement | Claim			66
Loss Contingency Class Action Claims Filed, Number of Apartments Included in Settlement Submitted | Claim			44
Loss Contingency Class Action Claims Filed, Number of Apartments Included in Settlement Submitted Amount | $			$ 6,900
Loss Contingency Class Action Claims Filed, Number of Apartments Issued Awards By Claims Adjuster | Claim			35
Loss Contingency Class Action Claims Filed, Timing Remaining for Claim Evaluation			2 months
Loss Contingency Class Action Claims Filed, Number of Apartments in Settlement Previously Resolved | Claim			60
Loss Contingency Subrogation Claims Filed Pending Not Dismissed Number | Claim			1
Loss contingency, total class action claims filed number | Claim			4