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COMMITMENTS AND CONTINGENCIES (Details)	1 Months Ended		12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details)	Aug. 31, 2017 USD ($)	Jan. 31, 2016 shares	Dec. 31, 2018 USD ($) officer	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Commitments and contingencies
Outstanding loan commitments and approvals to fund loans			$ 8,405,000
Future obligations under leases to fund tenant improvements and in other future construction obligation			27,181,000
Assets held for sale			202,000
Restricted cash			22,512,000	$ 27,008,000	$ 32,160,000
Ground lease for one of the project
Commitments and contingencies
Rent expense			0	1,168,000	1,752,000
Office space in Dallas, Texas
Commitments and contingencies
Rent expense			253,000	$ 228,000	$ 226,000
Noncancelable minimum lease payments in year 2019			256,000
Noncancelable minimum lease payments in year 2020			$ 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
Executive officers \| 2015 Equity Incentive Plan \| Employment agreements
Commitments and contingencies
Common stock issued (in shares) \| shares		76,423
Unrecognized compensation expense			$ 0
Restricted cash for tenant improvement allowance
Commitments and contingencies
Restricted cash			$ 12,478,000