Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Weighted average interest rate of debt outstanding.

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No definition available.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of the fee for available but unused credit capacity under the credit facility.

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The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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The carrying amount, as of the date of the latest financial statement presented, of real estate owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

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The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

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Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 2) - USD ($)	1 Months Ended				3 Months Ended		9 Months Ended
	Aug. 31, 2020	May 31, 2020	Mar. 31, 2020	Feb. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Unsecured Debt							$ 958,681,000	$ 0
Gain (Loss) on Extinguishment of Debt					$ 105,000	$ (93,000)	(9,333,000)	$ (602,000)
Credit Facility					0		0		$ 0
Net carrying value of apartment communities and improved land parcels securing debt					1,455,524,000		1,455,524,000
Unsecured Notes 2.45 Percent [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount		$ 600,000,000
Proceeds from Issuance of Debt		593,430,000
Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Long-term Debt, Percentage Bearing Fixed Interest, Amount					409,649,000		409,649,000		479,221,000
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Long-term Debt, Percentage Bearing Fixed Interest, Amount					6,500,000,000		6,500,000,000		5,850,000,000
Unsecured Notes 2.30 Percent [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Face Amount				$ 700,000,000
Proceeds from Issuance of Debt				$ 694,701,000
Unsecured Notes 2.30 Percent [Member] \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage				2.30%
Floating Rate Unsecured Notes 300 Million [Member] \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Unsecured Debt		300,000,000
Gain (Loss) on Extinguishment of Debt		$ 268,000
Notes Payable 3.625 Maturities 2020 and 2021 [Member] \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Gain (Loss) on Extinguishment of Debt			$ 9,170,000
Unsecured Notes 2.45 Percent [Member] \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage		2.45%
Notes Payable Maturities 2021 [Member] \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage			3.95%
Repayments of Unsecured Debt			$ 250,000,000
Notes Payable Maturities 2020 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage	4.18%			3.08%
Line of Credit [Member]
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity					1,750,000,000		$ 1,750,000,000
Annual facility fee, percentage							0.125%
Annual facility fee							$ 2,188,000
Credit Facility					0		0		0
Outstanding balance of letters of credit					$ 3,752,000		$ 3,752,000		11,488,000
Line of Credit [Member] \| LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)							0.775%
Current interest rate (as a percent)					0.92%		0.92%
Other Letter of Credit [Member]
Notes Payable, Unsecured Notes and Credit Facility
Outstanding balance of letters of credit					$ 31,822,000		$ 31,822,000		$ 24,939,000
Fixed Rate Mortgage Notes Payable [Member]
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)					3.80%		3.80%		3.90%
Notes Payable Maturities 2027
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage				2.38%
Notes Payable Maturities 2027 \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage					3.35%		3.35%
Notes Payable 3.625 Maturities 2020 [Member] \| Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Debt Instrument, Interest Rate, Stated Percentage			3.625%
Repayments of Unsecured Debt			$ 400,000,000
Variable Rate Mortgage Notes Payable Unsecured Term Loan and Credit Facility [Member]
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)					1.70%		1.70%		3.20%
Avalon San Bruno III [Member] \| Notes Payable Maturities 2027 \| Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Long-term Debt, Percentage Bearing Fixed Interest, Amount				$ 51,000,000
Avalon Hoboken [Member] \| Notes Payable Maturities 2020, Fixed Rate [Member] \| Secured Debt [Member]
Notes Payable, Unsecured Notes and Credit Facility
Repayments of Secured Debt	$ 67,904,000