UNSECURED BANK CREDIT FACILITIES (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) Integer	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Unsecured bank credit facilities, net of debt issuance costs	$ 168,454,000	$ 207,066,000
Average bank borrowings	$ 182,478,000	$ 95,629,000	$ 87,095,000
Weighted average interest rates (in hundredths)	2.32%	1.01%	1.86%
Amortization of facility fees	$ 713,000	$ 751,000	$ 790,000
Amortization of debt issuance costs	$ 650,000	606,000	$ 561,000
Moody's Credit Rating	Baa2
Former bank credit facility obtained in 2018 - $350 million | Nine bank group unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Borrowing Capacity		$ 350,000,000
Debt instrument, margin (in basis points)		100
Line of credit, facility fee (in basis points)		20
Debt Instrument, Maturity Date, Description		July 30, 2022
Former credit facility obtained in 2018 - $45 million [Member] | Pnc Na Unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Borrowing Capacity		$ 45,000,000
Debt instrument, margin (in basis points)		100
Line of credit, facility fee (in basis points)		20
Debt Instrument, Maturity Date, Description		July 30, 2022
$425 million credit facility - obtained in 2021 | Nine bank group unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Borrowing Capacity	$ 425,000,000
Debt instrument, margin (in basis points)	77.5
Line of credit, facility fee (in basis points)	15
Credit facility, extension option	two six-month extensions
Banks included in the unsecured revolving credit facility group | Integer	9
Line of Credit Facility, Interest Rate at Period End	5.146%
Unsecured bank credit facilities - variable rate, carrying amount	$ 170,000,000
Letters of Credit Outstanding, Amount	$ 67,000
Debt Instrument, Maturity Date	Jul. 30, 2025
Line of credit facility, accordion	$ 325,000,000
$50 million credit facility - obtained in 2021 | Pnc Na Unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Borrowing Capacity	$ 50,000,000
Debt instrument, margin (in basis points)	77.5
Line of credit, facility fee (in basis points)	15
Credit facility, extension option	two six-month extensions
Line of Credit Facility, Interest Rate at Period End	5.167%
Unsecured bank credit facilities - variable rate, carrying amount	$ 0
Line of Credit Facility, Expiration Date	Jul. 30, 2025
Bank credit facility obtained in 2021 - $425 and $50 million | Nine bank group unsecured revolving credit facility [Member]
Line of Credit Facility [Line Items]
Sustainability-linked pricing component, interest margin reduction (in basis points)	1
Credit rating basis for initial pricing basis, credit facilities	BBB+/Baa1
Line of Credit Facility Covenant Terms, Consolidated Leverage Ratio	32.50%