SIGNIFICANT ACCOUNTING POLICIES (Details) - joint_ventures	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Controlling interest Joint ventures [Abstract]
Joint Ventures	1	1	2
University Business Center 120 and 130 [Member]
Controlling interest Joint ventures [Abstract]
Controlling interest in joint ventures (in hundredths)	80.00%
Joint ventures' assets, liabilities, revenues and expenses with noncontrolling interests (in hundredths)	100.00%
University Business Center [Member]
Controlling interest Joint ventures [Abstract]
Controlling interest in joint ventures (in hundredths)		80.00%	80.00%
Noncontrolling Interest, Ownership Percentage acquired during period	20.00%
Joint ventures' assets, liabilities, revenues and expenses with noncontrolling interests (in hundredths)	100.00%	100.00%	100.00%
Castilian Research Center [Member]
Controlling interest Joint ventures [Abstract]
Controlling interest in joint ventures (in hundredths)			80.00%
Joint ventures' assets, liabilities, revenues and expenses with noncontrolling interests (in hundredths)		100.00%	100.00%
Industry Distribution Center II - undivided tenant [Member]
Tenant-in-common interest [Abstract]
Equity method of accounting is used for undivided tenant-in-common interest in Industry Distribution Center II (in hundredths)	50.00%	50.00%	50.00%