RELATED PARTY TRANSACTIONS - Additional Information (Details)				3 Months Ended		6 Months Ended		12 Months Ended	127 Months Ended
	Nov. 01, 2019	Oct. 29, 2019	Mar. 20, 2019 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) unit shares	Jun. 30, 2020 USD ($) shares	Jul. 01, 2020 shares	Dec. 31, 2018 USD ($)	May 12, 2017 USD ($)	Oct. 28, 2016 USD ($)
Related Party Transaction [Line Items]
Redemptions of common stock			$ 8,600,000	$ 356,000	$ 2,568,000	$ 824,000	$ 5,107,000		$ 286,200,000
Investments in unconsolidated entities				$ 78,478,000		$ 78,478,000		$ 78,276,000	$ 78,478,000
DayMark Service Entities
Related Party Transaction [Line Items]
Property management fee, percent of gross asset value fee			1.50%
Annual property management fee, percent of tenants rent received fee			8.00%
Acquisition fee, percent of purchase price fee			1.00%
Commission fee from sales as broker			1.00%
KBS Capital Advisors LLC | Subordinated Performance Fee Due Upon Termination
Related Party Transaction [Line Items]
Issuance of restricted stock (in shares) | shares						3,411,737
Period of redemption after vesting						60 days
Termination fee as percent of liquidation proceeds, percent				50.00%		50.00%			50.00%
Percent of total operating expenses in four consecutive quarters				2.00%		2.00%			2.00%
Percent of total operating expenses in four consecutive quarters, benchmark				25.00%		25.00%			25.00%
KBS Capital Advisors LLC | Subordinated Performance Fee Due Upon Termination | After November 1, 2024
Related Party Transaction [Line Items]
Period of redemption of remaining shares						60 days
DayMark | Battery Point Holdings
Related Party Transaction [Line Items]
Noncontrolling interest			40.00%
Point Trust LLC
Related Party Transaction [Line Items]
Investment acquired (in shares) | shares			210,000
Investment acquired (in dollars per shares) | $ / shares			$ 25
Series B Preferred Units | Point Trust LLC
Related Party Transaction [Line Items]
Redemptions of common stock (in shares) | shares			13,000
Redemptions of common stock (in dollars per shares) | $ / shares			$ 1,000
Principal paydown			$ 900,000
Point Trust LLC
Related Party Transaction [Line Items]
Investment acquired (in shares) | shares			210,000
Investment acquired (in dollars per shares) | $ / shares			$ 25
Number of shares purchased (in shares) | shares								430,000
Stock repurchased during period								$ 10,800,000
Point Trust LLC | Series B Preferred Units
Related Party Transaction [Line Items]
Investments to be made												$ 17,500,000
Investments											$ 4,500,000
Dividend rate, percentage		12.00%
Redemptions of common stock (in shares) | shares			13,000
Redemptions of common stock (in dollars per shares) | $ / shares			$ 1,000
Point Trust LLC | Series B Preferred Units | Maximum
Related Party Transaction [Line Items]
Investments to be made													$ 25,000,000
Point Trust LLC | Series A-3 Preferred Units
Related Party Transaction [Line Items]
Investments			$ 5,300,000
Principal paydown			$ 7,700,000
Investment acquired (in shares) | shares				640,000		640,000			640,000
Number of shares purchased (in shares) | shares								430,000
Stock repurchased during period								$ 10,800,000
Investments in unconsolidated entities				$ 14,000,000.0		$ 14,000,000.0			$ 14,000,000.0
Point Trust LLC | Series A-3 Preferred Units | Subsequent Event
Related Party Transaction [Line Items]
Shares eliminated in consolidation due to acquisition | shares										640,000
Pacific Oak Opportunity Zone Fund I
Related Party Transaction [Line Items]
Investments								$ 20,600,000
Acquisition fee, percent of purchase price fee								1.50%
Investments in unconsolidated entities				21,280,000		21,280,000		$ 20,846,000	21,280,000
Number of units in real estate property | unit								91
Investment, purchase price, benchmark								$ 25,000,000.0
Acquisition fee of purchase price fee in excess of benchmark purchase price								1.00%
Asset management fee, percent								0.25%
Financing fee as percent of original principal amount of any indebtedness								0.50%
Battery Point Series A-3 Preferred Units
Related Party Transaction [Line Items]
Investments in unconsolidated entities				13,991,000		13,991,000		$ 13,991,000	13,991,000
Battery Point Series A-3 Preferred Units | Series A-3 Preferred Units
Related Party Transaction [Line Items]
Investments in unconsolidated entities				$ 14,000,000.0		$ 14,000,000.0			$ 14,000,000.0
Pacific Oak Capital Advisors LLC
Related Party Transaction [Line Items]
Term of advisory agreement	1 year
Advisory agreement, renewal period	1 year