DEBT (Details) - USD ($)		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Secured and Unsecured Debt [Line Items]
Unsecured bank credit facilities, change during period		$ 25,653,000
Proceeds from unsecured bank credit facilities		281,342,000	$ 444,314,000
Repayments of Bank Debt		255,988,000	$ 388,569,000
Loans Payable, Noncurrent [Abstract]
Secured Debt		202,178,000		$ 257,505,000
Unsecured Debt		653,178,000		652,838,000
Unsecured bank credit facilities		216,643,000		190,990,000
Total debt		1,071,999,000		1,101,333,000
Secured and unsecured debt [Member]
Loans Payable, Noncurrent [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Remainder of Fiscal Year		2,736,000
Payments of principal over future years [Abstract]
2018		61,316,000
2019		130,569,000
2020		114,096,000
2021		129,563,000
2022 and beyond		419,813,000
Long-term debt, maturities, secured debt and unsecured debt		858,093,000
Unsecured Debt [Member]
Secured and Unsecured Debt [Line Items]
Unsecured debt, change during period		340,000
Secured Debt [Member]
Secured and Unsecured Debt [Line Items]
Secured debt, change during period		(55,327,000)
Secured debt, amount repaid during period		45,069,000
Secured debt, principal payments during period		10,409,000
Unsecured bank credit facilities
Loans Payable, Noncurrent [Abstract]
Unsecured bank credit facilities - variable rate, carrying amount		137,374,000		112,020,000
Unsecured bank credit facilities - fixed rate, carrying amount	[1]	80,000,000		80,000,000
Unamortized debt issuance costs		(731,000)		(1,030,000)
Unsecured bank credit facilities		216,643,000		190,990,000
Unsecured Debt [Member]
Loans Payable, Noncurrent [Abstract]
Unsecured debt, carrying amount	[1]	655,000,000		655,000,000
Unamortized debt issuance costs		(1,822,000)		(2,162,000)
Unsecured Debt		653,178,000		652,838,000
Secured Debt [Member]
Loans Payable, Noncurrent [Abstract]
Secured debt, carrying amount	[1]	203,093,000		258,594,000
Unamortized debt issuance costs		(915,000)		(1,089,000)
Secured Debt		$ 202,178,000		$ 257,505,000

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