Organization, Basis of Presentation, and Significant Accounting Policies (Details 3)	12 Months Ended
	Dec. 31, 2020 USD ($) community home $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Basic and diluted shares outstanding
Weighted average common shares—basic | shares	140,094,722	139,054,191	137,844,755
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500	7,500
Effect of dilutive securities (in shares) | shares	332,973	509,859	436,986
Weighted average common shares - diluted (in shares) | shares	140,435,195	139,571,550	138,289,241
Calculation of Earnings per Share—basic
Net Income (Loss) Available to Common Stockholders, Basic	$ 827,630,000	$ 785,974,000	$ 974,525,000
Net income allocated to unvested restricted shares	(1,955,000)	(2,063,000)	(2,839,000)
Net income attributable to common stockholders, adjusted	$ 825,675,000	$ 783,911,000	$ 971,686,000
Weighted average common shares—basic | shares	140,094,722	139,054,191	137,844,755
Earnings per common share - basic (in dollars per share) | $ / shares	$ 5.89	$ 5.64	$ 7.05
Calculation of Earnings per Share—diluted
Net Income (Loss) Available to Common Stockholders, Basic	$ 827,630,000	$ 785,974,000	$ 974,525,000
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships, including discontinued operations	48,000	46,000	44,000
Adjusted net income attributable to common stockholders	$ 827,678,000	$ 786,020,000	$ 974,569,000
Weighted average common shares—diluted | shares	140,435,195	139,571,550	138,289,241
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 5.89	$ 5.63	$ 7.05
Real Estate [Line Items]
Operating Lease, Lease Income	$ 2,297,442,000	$ 2,319,666,000	$ 2,280,963,000
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Abandoned pursuits costs	12,317,000	4,896,000	4,388,000
Casualty and impairment loss, net	0	0	215,000
Impairment of investment in unconsolidated entities	0	0	0
Management, development and other fees	3,819,000	4,960,000	3,572,000
Revenues	$ 2,301,261,000	2,324,626,000	2,284,535,000
Number of real estate properties | community	273
Number of Units in Real Estate Property | home	80,094
New York City, NY
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Abandoned pursuits costs	$ 7,264,000
Land
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Casualty and impairment loss, net	0	0	826,000
Continuing Operations
Real Estate [Line Items]
Operating Lease, Lease Income	2,242,282,000	2,236,405,000	2,084,704,000
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	13,643,000	13,612,000	9,818,000
Business interruption insurance proceeds	385,000	1,441,000	26,000
Revenues	2,256,310,000	2,251,458,000	2,094,548,000
Management, Development And Other [Member] | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	3,819,000	4,960,000	3,572,000
Rental and non-rental related income | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	9,824,000	8,652,000	6,246,000
Corporate, Non-Segment [Member]
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Revenues	3,819,000	4,960,000	3,572,000
Corporate, Non-Segment [Member] | Continuing Operations
Real Estate [Line Items]
Operating Lease, Lease Income	0	0	0
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	3,819,000	4,960,000	3,572,000
Business interruption insurance proceeds	0	0	0
Revenues	3,819,000	4,960,000	3,572,000
Corporate, Non-Segment [Member] | Management, Development And Other [Member] | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	3,819,000	4,960,000	3,572,000
Corporate, Non-Segment [Member] | Rental and non-rental related income | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	0	0	0
Established Communities | Operating segment
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Revenues	2,028,317,000	2,107,288,000	1,731,570,000
Established Communities | Operating segment | Continuing Operations
Real Estate [Line Items]
Operating Lease, Lease Income	2,021,232,000	2,099,273,000	1,727,299,000
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	6,970,000	7,028,000	4,245,000
Business interruption insurance proceeds	115,000	987,000	26,000
Revenues	2,028,317,000	2,107,288,000	1,731,570,000
Established Communities | Operating segment | Management, Development And Other [Member] | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	0	0	0
Established Communities | Operating segment | Rental and non-rental related income | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	6,970,000	7,028,000	4,245,000
Other Stabilized Communities | Operating segment
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Revenues	140,173,000	110,434,000	238,584,000
Other Stabilized Communities | Operating segment | Continuing Operations
Real Estate [Line Items]
Operating Lease, Lease Income	138,113,000	108,756,000	236,852,000
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	1,790,000	1,224,000	1,732,000
Business interruption insurance proceeds	270,000	454,000	0
Revenues	140,173,000	110,434,000	238,584,000
Other Stabilized Communities | Operating segment | Management, Development And Other [Member] | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	0	0	0
Other Stabilized Communities | Operating segment | Rental and non-rental related income | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	1,790,000	1,224,000	1,732,000
Development/Redevelopment Communities | Operating segment | Continuing Operations
Real Estate [Line Items]
Operating Lease, Lease Income	82,937,000	28,376,000	120,553,000
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	1,064,000	400,000	269,000
Business interruption insurance proceeds	0	0	0
Revenues	84,001,000	28,776,000	120,822,000
Development/Redevelopment Communities | Operating segment | Management, Development And Other [Member] | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	0	0	0
Development/Redevelopment Communities | Operating segment | Rental and non-rental related income | Continuing Operations
Casualty Loss, Abandoned Pursuit Costs and Impairment of Long-Lived Assets
Management, development and other fees	$ 1,064,000	$ 400,000	$ 269,000