REAL ESTATE HELD FOR SALE (Narrative) (Details) - property	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018
Office Properties
Real Estate Properties [Line Items]
Number of real estate properties		8
Office Properties | Disposed of by Sale
Real Estate Properties [Line Items]
Number of real estate properties sold	2
Office Buildings, Campus
Real Estate Properties [Line Items]
Number of real estate properties		8
Office Buildings, Campus | Held-for-sale
Real Estate Properties [Line Items]
Number of real estate properties		2