COMMITMENTS AND CONTINGENCIES (Details)	1 Months Ended	12 Months Ended
	Aug. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) officer	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments and contingencies
Outstanding loan commitments and approvals to fund loans		$ 9,696,000
Future obligations under leases to fund tenant improvements and in other future construction obligation		7,747,000
Restricted cash		12,146,000	$ 22,512,000	$ 27,008,000
Operating lease, right-of-use asset		106,000
Operating lease, liability		106,000
Ground lease for one of the project
Commitments and contingencies
Rent expense		0
Rent expense			0	1,168,000
Office space in Dallas, Texas
Commitments and contingencies
Rent expense		294,000
Rent expense			$ 253,000	$ 228,000
Noncancelable minimum lease payments		$ 106,000
Pending litigation | City and County of San Francisco Real Property Transfer Tax Case
Commitments and contingencies
Penalties, interest, and legal fees paid	$ 11,845,000
Executive officers | Employment agreements
Commitments and contingencies
Multiplier to annual base salary paid in event of death		2
Multiplier to annual base salary paid in event of disability		1
Executive officers | 2015 Equity Incentive Plan
Commitments and contingencies
Number of officers covered under employment agreement | officer		2
Restricted cash for tenant improvement allowance
Commitments and contingencies
Restricted cash		$ 2,814,000