ORGANIZATION (Details) $ in Millions	8 Months Ended	9 Months Ended
	Sep. 30, 2020 USD ($) property shares	Sep. 30, 2020 property shares	Jan. 31, 2020 property shares	Dec. 31, 2019 shares	Sep. 30, 2019 shares	Jun. 30, 2019 shares	Dec. 31, 2018 shares
Organizational Structure [Line Items]
Common stock, shares issued (in shares) | shares	184,545,636	184,545,636		185,302,037
Common stock, shares outstanding (in shares) | shares	184,545,636	184,545,636		185,302,037
Number of tenants with rent relief, COVID-19 | property	4	4
Common Stock
Organizational Structure [Line Items]
Common stock, shares outstanding (in shares) | shares			185,228,220	185,302,037	185,551,436	185,871,023	186,464,794
KBS Capital Advisors LLC
Organizational Structure [Line Items]
Period of Advisory Agreement renewal		1 year
Period of termination notice		60 days
KBS Capital Advisors LLC |  Common Stock
Organizational Structure [Line Items]
Shares held by affiliate | shares	20,000	20,000
Office Properties
Organizational Structure [Line Items]
Number of real estate properties | property	4	4
Decrease in real estate property values, COVID-19 | $	$ 71.2
Office Campus
Organizational Structure [Line Items]
Number of real estate properties | property	1	1	1
Office Buildings, Campus
Organizational Structure [Line Items]
Number of real estate properties | property	2	2
KBS Limited Partnership II
Organizational Structure [Line Items]
Partnership interest in Operating Partnership		0.10%
Partnership interest in the Operating Partnership and is its sole limited partner		99.90%