REAL ESTATE SOLD AND HELD FOR SALE DISCONTINUED OPERATIONS (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) ft² a	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) ft² a Integer
Long Lived Assets Held-for-sale [Line Items]
Number of real estate properties transferred to held for sale and sold | Integer			2
2017 Operating Property Sales (Stemmons Circle, Techway Southwest I-IV) [Member]
Long Lived Assets Held-for-sale [Line Items]
Square Footage of Real Estate Property | ft²			514,000
Gain (Loss) on Sale of Properties			$ 21,900,000
Proceeds from Sale of Property, Plant, and Equipment			$ 38,000,000
2018 Operating Property Sales [Member]
Long Lived Assets Held-for-sale [Line Items]
Square Footage of Real Estate Property | ft²	214,000
Gain (Loss) on Sale of Properties	$ 10,200,000
Proceeds from Sale of Property, Plant, and Equipment	$ 14,900,000
Land [Member]
Long Lived Assets Held-for-sale [Line Items]
SIze (in acres) of land sold | a	11		19
Proceeds from Sale of Property, Plant, and Equipment	$ 2,577,000		$ 3,778,000
Loss on sales of land		$ (40,000)
Gain on sales of land	$ 86,000		$ 293,000