REAL ESTATE EQUITY SECURITIES - Shares Owned (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Number of Shares Owned (in shares)	70,897,649	67,354,922
Total Carrying Value	$ 84,365	$ 81,439
Kepple Pacific Oak US REIT
Debt Securities, Available-for-sale [Line Items]
Number of Shares Owned (in shares)	64,165,352	64,165,352
Total Carrying Value	$ 46,520	$ 50,049
Franklin Street Properties Corp.
Debt Securities, Available-for-sale [Line Items]
Number of Shares Owned (in shares)	5,211,021	2,773,729
Total Carrying Value	$ 19,072	$ 23,743
Plymouth Industrial REIT, Inc.
Debt Securities, Available-for-sale [Line Items]
Number of Shares Owned (in shares)	1,521,276	415,841
Total Carrying Value	$ 18,773	$ 7,647