Organization, Basis of Presentation, and Significant Accounting Policies (Details 3) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended			15 Months Ended
	Dec. 31, 2016 USD ($) community land_parcel home building $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2016 USD ($) community land_parcel home building $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Mar. 31, 2016 USD ($)
Basic and diluted shares outstanding
Weighted average common shares—basic | shares									136,928,251	133,565,711	130,586,718
Weighted average DownREIT units outstanding (in shares) | shares									7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares									525,886	1,019,966	643,284
Weighted average common shares - diluted (in shares) | shares									137,461,637	134,593,177	131,237,502
Calculation of Earnings per Share—basic
Net income attributable to common stockholders	$ 242,235	$ 356,392	$ 197,444	$ 237,931	$ 155,428	$ 206,142	$ 172,324	$ 208,144	$ 1,034,002	$ 742,038	$ 683,567
Net income allocated to unvested restricted shares									(2,610)	(1,774)	(1,523)
Net income attributable to common stockholders, adjusted									$ 1,031,392	$ 740,264	$ 682,044
Weighted average common shares—basic | shares									136,928,251	133,565,711	130,586,718
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.76	$ 2.60	$ 1.44	$ 1.73	$ 1.13	$ 1.54	$ 1.30	$ 1.57	$ 7.53	$ 5.54	$ 5.22
Calculation of Earnings per Share—diluted
Net income attributable to common stockholders	$ 242,235	$ 356,392	$ 197,444	$ 237,931	$ 155,428	$ 206,142	$ 172,324	$ 208,144	$ 1,034,002	$ 742,038	$ 683,567
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations									41	38	35
Adjusted net income attributable to common stockholders									$ 1,034,043	$ 742,076	$ 683,602
Weighted average common shares—diluted | shares									137,461,637	134,593,177	131,237,502
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.76	$ 2.59	$ 1.44	$ 1.73	$ 1.13	$ 1.53	$ 1.29	$ 1.56	$ 7.52	$ 5.51	$ 5.21
Dividends per common share: (in dollars per share) | $ / shares									$ 5.4	$ 5	$ 4.64
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Abandoned pursuits costs									$ 4,183	$ 3,016	$ 3,964
Casualty and impairment (gain) loss, net									$ (3,935)	(10,542)	0
Number of Land Parcels Impaired | land_parcel									3
Impairment of investment in unconsolidated entities									$ 0	0	0
Real Estate Investment Property, Net	$ 15,045,593				$ 13,847,526				15,045,593	13,847,526
Gain on Business Interruption Insurance Recovery									$ 20,564	1,509	$ 2,494
Number of Real Estate Properties | community	258								258
Number of Units in Real Estate Property | home	74,538								74,538
Number of Land Parcels Held For Sale | land_parcel	2								2
Land [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment (gain) loss, net									$ 10,500
Avalon at Edgewater [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment (gain) loss, net									(8,702)	(15,538)
Insurance Proceeds									29,008	44,142		$ 73,150
Real Estate Investment Property, Net					$ 21,844					21,844
Casualty Loss										6,760
Gain on Business Interruption Insurance Recovery									$ 20,306
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 Units in Real Estate Property | home	168								168
New England [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment (gain) loss, net									$ (5,732)
Insurance Proceeds									8,493
Casualty Loss									$ 2,761
New England [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment (gain) loss, net										4,195
New England [Member] | Avalon at Edgewater [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment (gain) loss, net										$ 26,039
Stock Options
Real Estate [Line Items]
Estimated forfeiture rate of stock options (as a percent)									0.80%