ORGANIZATION (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended	55 Months Ended	135 Months Ended
	Oct. 03, 2014 USD ($) shares	Nov. 30, 2021 property	Jan. 31, 2021 property	Jun. 30, 2022 USD ($) property shares	Jun. 30, 2021 USD ($) shares	Jun. 30, 2022 USD ($) property shares	Jun. 30, 2021 USD ($) shares	Dec. 31, 2021 property shares	May 29, 2015 USD ($) shares	Jun. 30, 2022 USD ($) property shares	Jan. 26, 2010 $ / shares shares
Organizational Structure [Line Items]
Common stock, shares issued (in shares)				147,273,576		147,273,576		153,150,766		147,273,576
Issuance of common stock | $				$ 9,139	$ 14,959	$ 15,405	$ 26,285
Redemptions of common stock | $				$ 36,956	$ 2,971	$ 76,621	$ 6,083
Private Placement
Organizational Structure [Line Items]
Issuance of common stock (in shares)	258,462
Issuance of common stock | $	$ 2,400
Held-for-sale
Organizational Structure [Line Items]
Number of real estate properties | property				0		0				0
Disposed of by Sale
Organizational Structure [Line Items]
Number of real estate properties disposed | property		1	1					2
Office Properties
Organizational Structure [Line Items]
Number of real estate properties | property				16		16				16
Mixed-use Office/Retail Property
Organizational Structure [Line Items]
Number of real estate properties | property				1		1				1
Common Stock
Organizational Structure [Line Items]
Issuance of common stock (in shares)				892,341	1,463,769	1,504,393	2,573,027		169,006,162
Issuance of common stock | $				$ 10	$ 14	$ 15	$ 26		$ 1,700,000
Shares of common stock sold under dividend reinvestment plan, shares										42,324,144
Shares of common stock sold under dividend reinvestment plan, value | $										$ 437,100
Redemptions of common stock (in shares)				3,560,280	276,362	7,381,583	566,101			72,056,406
Redemptions of common stock | $				$ 36	$ 3	$ 74	$ 6			$ 764,500
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 Capital Advisors LLC | Common Stock
Organizational Structure [Line Items]
Shares held by affiliate (in shares)				20,857		20,857				20,857
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%