COMMITMENTS AND CONTINGENCIES (Details)	1 Months Ended		12 Months Ended
	Aug. 31, 2017 USD ($)	Jan. 31, 2016 shares	Dec. 31, 2017 USD ($) officer	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2017
Commitments and contingencies
Outstanding loan commitments and approvals to fund loans			$ 16,054,000
Future obligations under leases to fund tenant improvements and in other future construction obligation			23,836,000
Restricted cash			27,008,000	$ 32,160,000
Ground lease for one of the project
Commitments and contingencies
Rent expense			1,168,000	1,752,000	$ 1,752,000
Straight line rent liability				13,289,000
Office space in Dallas, Texas
Commitments and contingencies
Rent expense			228,000	226,000	235,000
Noncancelable minimum lease payments in year 2018			253,000
Noncancelable minimum lease payments in year 2019			$ 106,000
Executive officers | 2015 Equity Incentive Plan
Commitments and contingencies
Number of employees covered under employment agreement | officer			2
Employment agreements | Executive officers
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
Employment agreements | Executive officers | 2015 Equity Incentive Plan
Commitments and contingencies
Common stock issued (in shares) | shares		76,423
Accrued payroll taxes					444,000
Stock-based compensation expense			$ 0	$ 0	$ 1,263,000
Unrecognized compensation expense			0
Restricted cash for tenant improvement allowance
Commitments and contingencies
Restricted cash			$ 11,103,000
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