Organization and Basis of Presentation (Details 3) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013 community	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 property community	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2008
Basic and diluted shares outstanding
Weighted average common shares - basic									126,855,754	97,416,401	89,922,465
Weighted average DownREIT units outstanding (in shares)									7,500	7,500	8,322
Effect of dilutive securities (in shares)									402,649	601,251	846,675
Weighted average common shares - diluted									127,265,903	98,025,152	90,777,462
Calculation of Earnings per Share - basic
Net income attributable to common stockholders	$ 252,212,000	$ (10,715,000)	$ 36,218,000	$ 75,427,000	$ 122,356,000	$ 86,844,000	$ 156,909,000	$ 57,758,000	$ 353,141,000	$ 423,869,000	$ 441,622,000
Net income allocated to unvested restricted shares									(563,000)	(1,264,000)	(1,631,000)
Net income attributable to common stockholders, adjusted									352,578,000	422,605,000	439,991,000
Weighted average common shares - basic									126,855,754	97,416,401	89,922,465
Earnings per common share - basic (in dollars per share)	$ 1.95	$ (0.08)	$ 0.28	$ 0.63	$ 1.19	$ 0.89	$ 1.64	$ 0.61	$ 2.78	$ 4.34	$ 4.89
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders	252,212,000	(10,715,000)	36,218,000	75,427,000	122,356,000	86,844,000	156,909,000	57,758,000	353,141,000	423,869,000	441,622,000
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations									32,000	28,000	27,000
Adjusted net income attributable to common stockholders									353,173,000	423,897,000	441,649,000
Weighted average common shares - diluted									127,265,903	98,025,152	90,777,462
Earnings per common share - diluted (in dollars per share)	$ 1.95	$ (0.08)	$ 0.28	$ 0.63	$ 1.19	$ 0.89	$ 1.63	$ 0.60	$ 2.78	$ 4.32	$ 4.87
Dividends per common share: (in dollars per share)									$ 4.28	$ 3.88	$ 3.57
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
Casualty and impairment loss										1,449,000	14,052,000
Abandoned pursuits costs									998,000	1,757,000	1,957,000
Number of impaired parcels of land									2
Impairment of land parcels											12,097,000	9,952,000
Impairment of investment in unconsolidated entities									0	0	1,955,000
Assets Held for Sale & Discontinued Operations
Number of operating communities that qualified for held for sale presentation	1								1
Derivative Instruments and Hedging Activities
Loss on interest rate contract									$ 51,000,000
Noncontrolling interests
Maximum ownership interest percentage in joint venture	100.00%								100.00%