DEBT (Details)		3 Months Ended
		Mar. 31, 2022 USD ($) basisPoints Integer	Dec. 31, 2021 USD ($)
Secured and Unsecured Debt [Line Items]
Moody's Credit Rating		Baa2
Unsecured bank credit facilities		$ 195,317,000	$ 207,066,000
Secured Debt		2,115,000	2,142,000
Unsecured Debt		1,267,084,000	1,242,570,000
Total debt		1,464,516,000	1,451,778,000
Secured and unsecured debt, net of debt issuance costs [Member]
Payments of principal over future years [Abstract]
2022 - Remainder of year		87,000
2023		115,119,000
2024		120,122,000
2025		145,128,000
2026		141,672,000
2027 and beyond		750,000,000
Total		$ 1,272,128,000
$75 million unsecured term loan (repaid in 2022) [Member]
Secured and Unsecured Debt [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		3.03%
Unsecured debt, carrying amount repaid		$ 75,000,000
$100 million senior unsecured term loan (refinanced in 2022)
Secured and Unsecured Debt [Line Items]
Basis point reduction in credit spread | basisPoints		60
Debt instrument, basis spread above variable rate | basisPoints		85
Debt Instrument, Term		5 years
Fixed interest rate		1.80%
Unsecured debt, carrying amount		$ 100,000,000
$100 million senior unsecured term loan (new in 2022)
Secured and Unsecured Debt [Line Items]
Debt Instrument, Term		6 years 6 months
Debt Instrument, Interest Rate, Effective Percentage		3.06%
Debt Instrument, Basis Spread on Variable Rate		1.30%
Unsecured debt, carrying amount		$ 100,000,000
Unsecured bank credit facilities
Secured and Unsecured Debt [Line Items]
Unsecured bank credit facilities - variable rate, carrying amount		197,313,000	209,210,000
Unsecured bank credit facilities		195,317,000	207,066,000
Unamortized debt issuance costs		(1,996,000)	(2,144,000)
Unsecured Debt [Member]
Secured and Unsecured Debt [Line Items]
Unamortized debt issuance costs		(2,916,000)	(2,430,000)
Unsecured debt, carrying amount	[1]	1,270,000,000	1,245,000,000
Unsecured Debt		1,267,084,000	1,242,570,000
Secured Debt [Member]
Secured and Unsecured Debt [Line Items]
Secured debt-fixed rate, carrying amount	[1]	2,128,000	2,156,000
Secured Debt		2,115,000	2,142,000
Unamortized debt issuance costs		(13,000)	$ (14,000)
Nine bank group unsecured revolving credit facility [Member] | Former credit facility obtained in 2018 - $350 million [Member]
Secured and Unsecured Debt [Line Items]
Line of Credit Facility, Borrowing Capacity		$ 350,000,000
Debt instrument, basis spread above variable rate		100
Line of credit, facility fee (in basis points)		20
Debt Instrument, Maturity Date, Description		July 30, 2022
Nine bank group unsecured revolving credit facility [Member] | Bank credit facility obtained in 2021 - $425 million
Secured and Unsecured Debt [Line Items]
Line of Credit Facility, Interest Rate at Period End		1.168%
Line of Credit Facility, Borrowing Capacity		$ 425,000,000
Number of banks included in the unsecured revolving credit facility | Integer		9
Debt instrument, basis spread above variable rate		77.5
Line of credit, facility fee (in basis points)		15
Debt Instrument, Maturity Date, Description		July 30, 2025
Extension option on credit facility		two six-month extensions
Line of credit facility, accordion		$ 325,000,000
Unsecured bank credit facilities - variable rate, carrying amount		$ 183,000,000
Nine bank group unsecured revolving credit facility [Member] | Bank credit facilities obtained in 2021 - $425 and $50 million
Secured and Unsecured Debt [Line Items]
Sustainability performance linked basis point reduction (in basis points)		1
Initial pricing basis for credit facilities		BBB+/Baa1
Line of credit facility covenant terms, consolidated leverage ratio		32.50%
Pnc Na Unsecured revolving credit facility [Member] | Former credit facility obtained in 2018 - $45 million [Member]
Secured and Unsecured Debt [Line Items]
Line of Credit Facility, Borrowing Capacity		$ 45,000,000
Debt instrument, basis spread above variable rate		100
Line of credit, facility fee (in basis points)		20
Debt Instrument, Maturity Date, Description		July 30, 2022
Pnc Na Unsecured revolving credit facility [Member] | Bank credit facility obtained in 2021 - $50 million
Secured and Unsecured Debt [Line Items]
Line of Credit Facility, Interest Rate at Period End		1.227%
Line of Credit Facility, Borrowing Capacity		$ 50,000,000
Debt instrument, basis spread above variable rate		77.5
Line of credit, facility fee (in basis points)		15
Debt Instrument, Maturity Date, Description		July 30, 2025
Extension option on credit facility		two six-month extensions
Unsecured bank credit facilities - variable rate, carrying amount		$ 14,313,000

[1] These loans have a fixed interest rate or an effectively fixed interest rate due to interest rate swaps.