SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Impairment, Fees and Income Tax) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Related Party Transaction [Line Items]
Impairment of real estate	$ 0	$ 14,745,000	$ 0
Number of loans originated as investment | loan	1
Income tax	$ 0	$ (9,000)	$ 48,000
KBS Capital Advisors LLC
Related Party Transaction [Line Items]
Percent of net cash flows to be received by related party	15.00%
Percent of amount on common stock listing to be received by related party	15.00%
Acquisition and origination fees	2.60%
Monthly management fee, percent of cost and real estate property investment, including any debt financing on property	0.0833%
Monthly management fee, percent of cost of investment less debt secured by investments	0.1667%
Noncompounded return on invested capital as percent per year	7.00%
Noncompounded return on invested capital in equity as percent per year	7.00%
KBS Capital Advisors LLC or Affiliates
Related Party Transaction [Line Items]
Benchmark amount of contracted disposition sales price	$ 50,000,000
Disposition fee as percent of benchmark contract sales price	1.50%
Disposition fee amount of benchmark contract sales price	$ 750,000
Disposition fee as percent above benchmark contract sales price	1.00%
KBS Capital Advisors LLC, Affiliates or Unaffiliated Third Parties | Maximum
Related Party Transaction [Line Items]
Selling commissions fees paid, percent of sales price	6.00%