Amount of accumulated amortization of debt issuance costs.

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

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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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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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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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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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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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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 portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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Amount, before accumulated depreciation, of real estate investment by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate. Excludes real estate not held as investment or interest.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Notes Payable, Revolving Credit Facility, Interest and Amortization of Deferred Debt Costs - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Oct. 01, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Principal amount	$ 1,148,117,000		$ 1,200,000,000
Debt outstanding with fixed-rate	969,100,000		980,800,000
Debt outstanding with variable-rate	179,000,000.0		179,500,000
Carrying value of properties collateralizing mortgage notes	1,100,000,000		1,200,000,000
Outstanding line of credit	103,548,000		103,913,000
Notes payable	814,268,000		827,603,000
Principal amount	1,139,183,000
Unamortized deferred debt costs	8,934,000		9,300,000
Debt issuance costs amortization	8,900,000		8,700,000
Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, remaining borrowing capacity	220,800,000
Outstanding line of credit	104,000,000.0		$ 104,500,000
Letter of Credit
Debt Instrument [Line Items]
Outstanding line of credit	185,000
New Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 400,000,000.0
New Facility \| Revolving Credit Facility \| LIBOR
Debt Instrument [Line Items]
Interest rate spread on LIBOR	1.40%
New Facility \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 325,000,000.0
New Facility \| Term Facility \| LIBOR
Debt Instrument [Line Items]
Interest rate spread on LIBOR	1.35%
New Facility \| Term Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 75,000,000.0
Park Van Ness Loan
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure	3,300,000
Notes payable	66,000,000.0
Park Van Ness Loan \| Subsequent Event
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure		$ 0
Broadlands Village Mortgage
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure	3,800,000
Principal amount	30,300,000
Avenel Business Park
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure	6,300,000
Avenel Business Park \| Mortgages
Debt Instrument [Line Items]
Principal amount	25,000,000.0
The Waycroft Mortgage
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure	23,600,000
The Waycroft Mortgage \| Mortgages
Debt Instrument [Line Items]
Principal amount	148,000,000.0
Ashbrook Marketplace Mortgage \| Mortgages
Debt Instrument [Line Items]
Principal amount	21,800,000
Kentlands Place Mortgage \| Mortgages
Debt Instrument [Line Items]
Principal amount	$ 29,600,000