REAL ESTATE PROPERTIES (Details)		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	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%
Depreciation Expense During the Period		$ 21,384,000	$ 18,960,000	$ 63,650,000	$ 55,785,000
Real Estate Properties
Land		418,346,000		418,346,000		$ 380,684,000
Building and building improvements		1,847,038,000		1,847,038,000		1,732,592,000
Tenant and other improvements		462,031,000		462,031,000		440,205,000
Right of use assets - Ground leases (operating)	[1]	12,242,000		12,242,000		0
Development and value-add properties	[2]	354,238,000		354,238,000		263,664,000
Real estate, development and value-add properties		3,093,895,000		3,093,895,000		2,817,145,000
Less accumulated depreciation		(854,368,000)		(854,368,000)		(814,915,000)
Real estate, net		2,239,527,000		$ 2,239,527,000		2,002,230,000
Ground Leases Disclosures [Abstract]
Weighted Average term for ground leases				44 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		261,000	$ 193,000	$ 705,000	$ 585,000	783,000
Operating Leases, Future Minimum Payments Due, Next Twelve Months		242,000		242,000		791,000
Operating Leases, Future Minimum Payments, Due in Two Years		970,000		970,000		791,000
Operating Leases, Future Minimum Payments, Due in Three Years		970,000		970,000		791,000
Operating Leases, Future Minimum Payments, Due in Four Years		970,000		970,000		791,000
Operating Leases, Future Minimum Payments, Due in Five Years		975,000		975,000		791,000
Operating Leases, Future Minimum Payments, Due Thereafter		39,914,000		39,914,000		30,751,000
Operating leases, future minimum payments due, total		44,041,000		44,041,000		$ 34,706,000
imputed interest related to right of use assets for ground leases	[3]	(31,538,000)		(31,538,000)
Amortization, ground leases		(228,000)		(228,000)
Ground Leases, Net		$ 12,275,000		$ 12,275,000
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
FLORIDA
Ground Leases Disclosures [Abstract]
Properties subject to ground leases		2		2
TEXAS
Ground Leases Disclosures [Abstract]
Properties subject to ground leases		3		3
ARIZONA
Ground Leases Disclosures [Abstract]
Properties subject to ground leases		1		1
Accounting Standards Update 2016-02 [Member]
Real Estate Properties
Right of use assets - Ground leases (operating)								$ 10,226,000
Logistics Center 6 & 7 [Member]
Real Estate Properties
Right of use assets - Ground leases (operating)							$ 2,679,000
Ground Leases Disclosures [Abstract]
Incremental borrowing rate used in determining the present value of lease payments							8.00%

[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, 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, to determine the imputed interest for its ground leases. The Company elected to use the portfolio approach as all of its ground leases in place as of January 1, 2019, have similar characteristics and determined 7.3% as the appropriate rate as of January 1, 2019, for all leases in place at that time. For the ground lease acquired during April 2019, the Company used its incremental borrowing rate, adjusted for the factors discussed above, which was determined to be 8.0%.