Organization and Basis of Presentation (Details 3) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014 home	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 home	Dec. 31, 2013	Dec. 31, 2012
Basic and diluted shares outstanding
Weighted average common shares—basic									130,586,718	126,855,754	97,416,401
Weighted average DownREIT units outstanding (in shares)									7,500	7,500	7,500
Effect of dilutive securities (in shares)									643,284	402,649	601,251
Weighted average common shares - diluted (in shares)									131,237,502	127,265,903	98,025,152
Calculation of Earnings per Share—basic
Net income attributable to common stockholders	$ 142,642,000	$ 241,100,000	$ 158,086,000	$ 141,739,000	$ 252,212,000	$ (10,715,000)	$ 36,218,000	$ 75,427,000	$ 683,567,000	$ 353,141,000	$ 423,869,000
Net income allocated to unvested restricted shares									(1,523,000)	(563,000)	(1,264,000)
Net income attributable to common stockholders, adjusted									682,044,000	352,578,000	422,605,000
Weighted average common shares—basic									130,586,718	126,855,754	97,416,401
Earnings per common share - basic (in dollars per share)	$ 1.08	$ 1.83	$ 1.22	$ 1.09	$ 1.95	$ (0.08)	$ 0.28	$ 0.63	$ 5.22	$ 2.78	$ 4.34
Calculation of Earnings per Share—diluted
Net income attributable to common stockholders	142,642,000	241,100,000	158,086,000	141,739,000	252,212,000	(10,715,000)	36,218,000	75,427,000	683,567,000	353,141,000	423,869,000
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations									35,000	32,000	28,000
Adjusted net income attributable to common stockholders									683,602,000	353,173,000	423,897,000
Weighted average common shares—diluted									131,237,502	127,265,903	98,025,152
Earnings per common share - diluted (in dollars per share)	$ 1.08	$ 1.83	$ 1.21	$ 1.09	$ 1.95	$ (0.08)	$ 0.28	$ 0.63	$ 5.21	$ 2.78	$ 4.32
Dividends per common share: (in dollars per share)									$ 4.64	$ 4.28	$ 3.88
Options to purchase shares of common stock excluded from computation of earnings per share amount (in shares)										605,899	396,346
Estimated forfeiture rate of stock options (as a percent)									1.40%
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Impairment of wholly-owned operating real estate assets									0	0	0
Abandoned pursuits costs									3,964,000	998,000	1,757,000
Impairment of Real Estate									0	0	0
Impairment of investment in unconsolidated entities									0	0	0
Casualty and impairment loss									0	0	1,449,000
Gain on business interruption insurance recovery									2,494,000	299,000	0
Number of communities held for sale	1								1
Derivative Instruments and Hedging Activities
Loss on interest rate contract									$ 0	$ 51,000,000	$ 0
Noncontrolling interests
Maximum Ownership Interest Percentage in Joint Venture	100.00%								100.00%