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, 2017 USD ($) community home building $ / shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) community home building $ / shares shares	Dec. 31, 2016 USD ($) land_parcel $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Mar. 31, 2016 USD ($)
Basic and diluted shares outstanding
Weighted average common shares—basic | shares									137,523,771	136,928,251	133,565,711
Weighted average DownREIT units outstanding (in shares) | shares									7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares									535,415	525,886	1,019,966
Weighted average common shares - diluted (in shares) | shares									138,066,686	137,461,637	134,593,177
Calculation of Earnings per Share—basic
Net income attributable to common stockholders	$ 237,573	$ 238,248	$ 165,225	$ 235,875	$ 242,235	$ 356,392	$ 197,444	$ 237,931	$ 876,921	$ 1,034,002	$ 742,038
Net income allocated to unvested restricted shares									(2,463)	(2,610)	(1,774)
Net income attributable to common stockholders, adjusted									$ 874,458	$ 1,031,392	$ 740,264
Weighted average common shares—basic | shares									137,523,771	136,928,251	133,565,711
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.72	$ 1.73	$ 1.20	$ 1.72	$ 1.76	$ 2.60	$ 1.44	$ 1.73	$ 6.36	$ 7.53	$ 5.54
Calculation of Earnings per Share—diluted
Net income attributable to common stockholders	$ 237,573	$ 238,248	$ 165,225	$ 235,875	$ 242,235	$ 356,392	$ 197,444	$ 237,931	$ 876,921	$ 1,034,002	$ 742,038
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations									42	41	38
Adjusted net income attributable to common stockholders									$ 876,963	$ 1,034,043	$ 742,076
Weighted average common shares—diluted | shares									138,066,686	137,461,637	134,593,177
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.72	$ 1.72	$ 1.20	$ 1.72	$ 1.76	$ 2.59	$ 1.44	$ 1.73	$ 6.35	$ 7.52	$ 5.51
Dividends per common share: (in dollars per share) | $ / shares									$ 5.68	$ 5.4	$ 5
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Abandoned pursuits costs									$ 2,370	$ 4,183	$ 3,016
Casualty and impairment loss (gain), net									6,250	$ (3,935)	(10,542)
Number of Land Parcels Impaired | land_parcel										3
Impairment of investment in unconsolidated entities									0	$ 0	0
Net operating real estate	$ 16,342,893				$ 15,045,593				16,342,893	15,045,593
Gain on Business Interruption Insurance Recovery									$ 3,498	20,564	1,509
Number of Real Estate Properties | community	267								267
Number of Units in Real Estate Property | home	77,614								77,614
Number of Land Parcels Held for Sale | community	0								0
Land [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss (gain), net									$ 9,350		0
Avalon at Edgewater [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss (gain), net										(8,702)	(15,538)
Insurance Proceeds										29,008	44,142	$ 73,150
Net operating real estate											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 loss (gain), net										(5,732)
Casualty Loss										2,761
Insurance Recoveries										8,493
Land Parcel [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss (gain), net										$ 10,500
Avalon Maplewood [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss (gain), net									$ 2,338
Insurance Proceeds									17,143
Net operating real estate	$ 16,361								16,361
Casualty Loss									19,481
Gain on Business Interruption Insurance Recovery									3,495
Other Nonrecurring Expense									3,120
Insurance Recoveries									$ 19,696
New England [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss (gain), net											4,195
New England [Member] | Avalon at Edgewater [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss (gain), net											$ 26,039