Organization, Basis of Presentation and Significant Accounting Policies (Details 2) - Long-term Debt, Type [Domain] $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) community home building $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) community Claim home Citation plaintiff building $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares
Loss Contingencies [Line Items]
Number of Real Estate Properties | community	257		257
Number of apartment homes included in operating apartment communities owned | home	74,857		74,857
Basic and diluted shares outstanding
Weighted average common shares - basic | shares	131,977,578	129,856,335	131,930,916	129,574,118
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares	1,101,361	384,486	1,192,947	356,614
Weighted average common shares - diluted | shares	133,086,439	130,248,321	133,131,363	129,938,232
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 172,324	$ 158,086	$ 380,469	$ 299,825
Net income allocated to unvested restricted shares	(445)	(254)	(975)	(487)
Net income attributable to common stockholders, adjusted	$ 171,879	$ 157,832	$ 379,494	$ 299,338
Weighted average common shares - basic | shares	131,977,578	129,856,335	131,930,916	129,574,118
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.30	$ 1.22	$ 2.88	$ 2.31
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	$ 172,324	$ 158,086	$ 380,469	$ 299,825
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	9	9	19	17
Adjusted net income available to common stockholders	$ 172,333	$ 158,095	$ 380,488	$ 299,842
Weighted average common shares - diluted | shares	133,086,439	130,248,321	133,131,363	129,938,232
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.29	$ 1.21	$ 2.86	$ 2.31
Options to purchase shares of common stock excluded from computation of earnings per share amount (in shares) | shares				243,326
Estimated forfeiture rate of stock options (as a percent)			1.00%
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 | Claim			4
Loss Contingency, Number of Plaintiffs | plaintiff			120
Loss Contingency, OSHA Citations | Citation			2
Loss Contingency, Insurance, Percentage Of Policy Amount Company Is Obligated To Fund	12.00%		12.00%
Loss Contingency, Insurance, Policy Amount For Calculating Self-Insurance Liability	$ 50,000		$ 50,000