ORGANIZATION (Details) $ / shares in Units, $ in Thousands		3 Months Ended		67 Months Ended	108 Months Ended
	Oct. 03, 2014 USD ($) shares	Mar. 31, 2020 USD ($) numberOfProperties shares	Mar. 31, 2019 USD ($) shares	May 29, 2016 USD ($) shares	Mar. 31, 2020 USD ($) numberOfProperties shares	Dec. 31, 2019 shares	Jan. 26, 2010 $ / shares shares
Organizational Structure [Line Items]
Common stock, shares issued (in shares)		181,784,482			181,784,482	180,970,743
Issuance of common stock | $		$ 11,904	$ 13,497
Redemptions of common stock | $		$ 3,049	$ 52,606
Private Placement
Organizational Structure [Line Items]
Issuance of common stock (in shares)	258,462
Issuance of common stock | $	$ 2,400
Office Properties
Organizational Structure [Line Items]
Number of real estate properties | numberOfProperties		18			18
Mixed-use Office/Retail Property
Organizational Structure [Line Items]
Number of real estate properties | numberOfProperties		1			1
Common Stock
Organizational Structure [Line Items]
Shares held by affiliate (in shares)		20,857			20,857
Issuance of common stock (in shares)		1,075,449	1,181,823	169,006,162
Issuance of common stock | $		$ 11	$ 12	$ 1,700,000
Shares of common stock sold under dividend reinvestment plan, shares					33,529,451
Shares of common stock sold under dividend reinvestment plan, value | $					$ 344,500
Redemptions of common stock (in shares)		261,710	4,594,982		28,750,807
Redemptions of common stock | $		$ 3	$ 46		$ 314,500
KBS Capital Advisors LLC
Organizational Structure [Line Items]
Common stock, shares issued (in shares)							20,000
Common stock, purchase price per share (in dollars per share) | $ / shares							$ 10.00
KBS Limited Partnership III
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%