Mortgage Notes Payable, Unsecured Notes and Credit Facility - Narrative (Details) - USD ($)	1 Months Ended			12 Months Ended
	Nov. 30, 2021	Sep. 30, 2021	Jan. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Repayment of unsecured debt				$ 462,147,000	$ 958,680,000	$ 0
Gain (Loss) on Extinguishment of Debt				(17,787,000)	(9,333,000)	$ (602,000)
Write off of Deferred Debt Issuance Cost		$ 5,743,000
Variable rate unsecured credit facility				0	0
Net carrying value of apartment communities and improved land parcels securing debt				$ 1,256,155,000
Percentage of principle amount at which the entity may redeem some or all of the notes				100.00%
Notes Payable Maturities 2021
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate (as a percent)			5.37%
Notes payable maturing in 2022
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Gain (Loss) on Extinguishment of Debt		$ 17,890,000
Notes Payable Maturities 2036
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate (as a percent)	3.79%
Variable rate unsecured credit facility
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity				$ 1,750,000,000
Line of credit facility, commitment fee percentage				0.125%
Annual facility fee				$ 2,188,000
Variable rate unsecured credit facility				0	0
Outstanding balance of letters of credit				$ 11,969,000	2,900,000
Variable rate unsecured credit facility | LIBOR
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)				0.775%
Debt instrument, interest rate, effective percentage				0.88%
Other Letter of Credit
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Outstanding balance of letters of credit				$ 39,581,000	$ 32,079,000
Fixed rate mortgage notes payable
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)				3.70%	3.80%
Variable rate mortgage notes payable, unsecured term loan and Credit Facility
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)				1.70%	1.70%
Secured notes | Notes Payable Maturities 2021 | Avalon San Bruno II
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured debt			$ 27,795,000
Secured notes | Notes Payable Maturities 2036 | Avalon Westbury
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured debt	$ 73,060,000
Unsecured notes | Minimum
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)				0.20%
Unsecured notes | Maximum
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)				0.45%
Unsecured notes | Notes payable maturing in 2022
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate (as a percent)		2.95%
Repayment of unsecured debt		$ 450,000,000
Prepayment Penalty		$ 12,147,000
Unsecured notes | Unsecured Notes 2.05 Percent
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate (as a percent)		2.05%
Unsecured notes | Unsecured Notes 1.90 Percent
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate (as a percent)	1.90%
Unsecured Notes 2.05 Percent
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Face amount, debt instrument		$ 700,000,000
Proceeds from Issuance of Debt		$ 694,617,000
Unsecured Notes 1.90 Percent
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Face amount, debt instrument	$ 400,000,000
Proceeds from Issuance of Debt	$ 396,976,000