REAL ESTATE PROPERTIES (Details)		3 Months Ended		12 Months Ended
		Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
Real Estate Properties [Line Items]
Percentage of occupancy to qualify as value-add property		75.00%
Percentage of acquisition price to be spent on capital items to qualify as value-add property		20.00%
Amortization expense for lease intangibles		$ 991,000	$ 1,012,000
Depreciation Expense During the Period		19,747,000	17,927,000
Real Estate Properties
Land		388,788,000		$ 380,684,000
Building and building improvements		1,762,694,000		1,732,592,000
Tenant and other improvements		448,391,000		440,205,000
Right of use assets - Ground leases (operating)	[1]	10,041,000		0
Development and value-add properties	[2]	264,526,000		263,664,000
Real estate, development and value-add properties		2,874,440,000		2,817,145,000
Less accumulated depreciation		(832,925,000)		(814,915,000)
Real estate, net		2,041,515,000		2,002,230,000
Rental Income Increase Decrease For Amortization Of Acquired In Place Lease Intangibles		(192,000)	(118,000)
Gain on casualties and involuntary conversion		$ 100,000	0
Ground Leases Disclosures [Abstract]
Weighted Average term for ground leases		45 years
Leases terms minimum		40 years
Leases terms maximum		50 years
Renewal period option minimum		15 years
Renewal period option maximum		35 years
Payment increase interval minimum		3 years
Payment increase interval maximum		10 years
Incremental borrowing rate used in determining the present value of lease payments					7.30%
Total ground lease expenditures for continuing and discontinued operations		$ 198,000	$ 195,000	783,000
Operating Leases, Future Minimum Payments Due, Next Twelve Months		593,000		791,000
Operating Leases, Future Minimum Payments, Due in Two Years		791,000		791,000
Operating Leases, Future Minimum Payments, Due in Three Years		791,000		791,000
Operating Leases, Future Minimum Payments, Due in Four Years		791,000		791,000
Operating Leases, Future Minimum Payments, Due in Five Years		791,000		791,000
Operating Leases, Future Minimum Payments, Due Thereafter		30,751,000		30,751,000
Operating leases, future minimum payments due, total		34,508,000		34,706,000
imputed interest related to right of use assets for ground leases	[3]	(24,283,000)
Amortization, ground leases		(184,000)
Ground Leases, Net		$ 10,041,000
Building [Member]
Real Estate Properties [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Minimum [Member] | Improvements [Member]
Real Estate Properties [Line Items]
Property, Plant and Equipment, Useful Life		3 years
Maximum [Member] | Improvements [Member]
Real Estate Properties [Line Items]
Property, Plant and Equipment, Useful Life		15 years
2018 Acquisitions [Member]
Real Estate Properties
Total cost of properties purchased				71,086,000
Amount of total cost allocated to land				23,263,000
Above Market Leases [Member] | 2018 Acquisitions [Member]
Real Estate Properties
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles				21,000
Below market lease [Member] | 2018 Acquisitions [Member]
Real Estate Properties
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles				1,756,000
Industrial Development [Member] | 2018 Acquisitions [Member]
Real Estate Properties
Amount of total cost allocated to real estate properties				$ 13,934,000
FLORIDA
Ground Leases Disclosures [Abstract]
Properties subject to ground leases		2
TEXAS
Ground Leases Disclosures [Abstract]
Properties subject to ground leases		2
ARIZONA
Ground Leases Disclosures [Abstract]
Properties subject to ground leases		1
Accounting Standards Update 2016-02 [Member]
Real Estate Properties
Right of use assets - Ground leases (operating)					$ 10,226,000

[1] See below and in Note 20 for information regarding the Company’s right of use assets for ground leases.

[2] Value-add properties are defined as properties that are either acquired but not stabilized or can be converted to a higher and better use.  Acquired properties meeting either of the following two conditions are considered value-add properties:  (1) Less than 75% occupied as of the acquisition date (or will be less than 75% occupied within one year of acquisition date based on near term lease roll), or (2) 20% or greater of the acquisition cost will be spent to redevelop the property.

[3] As the Company’s leases do not provide an implicit rate, in order to calculate the present value of the remaining ground lease payments, the Company used its incremental borrowing rate as of January 1, 2019, adjusted for a number of factors, including the long-term nature of the ground leases, the Company’s estimated borrowing costs, and the estimated fair value of the underlying land. The Company elected to use the portfolio approach as all of its ground leases have similar characteristics and determined 7.3% as the appropriate rate as of January 1, 2019.