Organization, Basis of Presentation, and Significant Accounting Policies (Details 3) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) home $ / shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares	Sep. 30, 2014 USD ($) $ / shares	Jun. 30, 2014 USD ($) $ / shares	Mar. 31, 2014 USD ($) $ / shares	Dec. 31, 2015 USD ($) home $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Basic and diluted shares outstanding
Weighted average common shares—basic | shares									133,565,711	130,586,718	126,855,754
Weighted average DownREIT units outstanding (in shares) | shares									7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares									1,019,966	643,284	402,649
Weighted average common shares - diluted (in shares) | shares									134,593,177	131,237,502	127,265,903
Calculation of Earnings per Share—basic
Net income attributable to common stockholders	$ 155,428	$ 206,142	$ 172,324	$ 208,144	$ 142,642	$ 241,100	$ 158,086	$ 141,739	$ 742,038	$ 683,567	$ 353,141
Net income allocated to unvested restricted shares									(1,774)	(1,523)	(563)
Net income attributable to common stockholders, adjusted									$ 740,264	$ 682,044	$ 352,578
Weighted average common shares—basic | shares									133,565,711	130,586,718	126,855,754
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.13	$ 1.54	$ 1.30	$ 1.57	$ 1.08	$ 1.83	$ 1.22	$ 1.09	$ 5.54	$ 5.22	$ 2.78
Calculation of Earnings per Share—diluted
Net income attributable to common stockholders	$ 155,428	$ 206,142	$ 172,324	$ 208,144	$ 142,642	$ 241,100	$ 158,086	$ 141,739	$ 742,038	$ 683,567	$ 353,141
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations									38	35	32
Adjusted net income attributable to common stockholders									$ 742,076	$ 683,602	$ 353,173
Weighted average common shares—diluted | shares									134,593,177	131,237,502	127,265,903
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.13	$ 1.53	$ 1.29	$ 1.56	$ 1.08	$ 1.83	$ 1.21	$ 1.09	$ 5.51	$ 5.21	$ 2.78
Dividends per common share: (in dollars per share) | $ / shares									$ 5	$ 4.64	$ 4.28
Options to purchase shares of common stock excluded from computation of earnings per share amount (in shares) | shares										605,899
Estimated forfeiture rate of stock options (as a percent)									1.00%
Number of communities held for sale | home	1								1
Derivative Instruments and Hedging Activities
Loss on interest rate contract									$ 0	$ 0	$ 51,000
Noncontrolling interests
Maximum Ownership Interest Percentage in Joint Venture	100.00%								100.00%
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Abandoned pursuits costs									$ 3,016	3,964	998
Impairment of investment in unconsolidated entities									0	0	0
Casualty (gain) loss and impairment loss, net									(10,542)	0	0
Real Estate Investment Property, Net	$ 13,847,526				$ 13,159,186				13,847,526	13,159,186
Gain on business interruption insurance recovery									1,509	$ 2,494	$ 299
Avalon at Edgewater [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty (gain) loss and impairment loss, net									(15,538)
Insurance Proceeds									44,142
Real Estate Investment Property, Net	$ 21,844								21,844
Casualty Loss									6,760
New England [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty (gain) loss and impairment loss, net									4,195
New England [Member] | Avalon at Edgewater [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty (gain) loss and impairment loss, net									$ 26,039