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COMMITMENTS AND CONTINGENCIES (Details)	1 Months Ended		3 Months Ended
COMMITMENTS AND CONTINGENCIES (Details)	Apr. 30, 2017 USD ($)	Jan. 31, 2016 shares	Mar. 31, 2017 USD ($) officer	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitments and contingencies
Outstanding loan commitments to fund loans			$ 11,784,000
Future obligations under leases to fund tenant improvements and other future construction obligation			39,362,000
Restricted cash			27,775,000		$ 32,160,000
Future noncancelable minimum lease payments
2017 (Nine months ending December 31, 2017)			562,000
2018			607,000
2019			503,000
2020			541,000
2021			578,000
Thereafter			127,101,000
Total			129,892,000
Ground Lease, Property One
Commitments and contingencies
Current annual rent			$ 503,000
Period after which the annual rental payment will be increased			5 years
Percentage increase in annual rental payment after every 5 years, option one			15.00%
Percentage increase in annual rental payment after every 5 years, percentage of CPI, option two			50.00%
Annual increase in rent payable on commencement dates			10.00%
Rent expense			$ 438,000	$ 438,000
Straight line rent liability			13,566,000		$ 13,289,000
Office Space in Dallas, Texas
Commitments and contingencies
Rent expense			$ 56,000	58,000
Employment agreements \| Executive Officers
Commitments and contingencies
Number of employees covered under employment agreement \| officer			2
Multiplier used for the calculation of payments in the event of death of employee			2
Multiplier used for the calculation of payments in the event of disability to employee			1
Employment agreements \| Executive Officers \| 2015 Equity Incentive Plan
Commitments and contingencies
Shares of common stock issued under incentive plan (in shares) \| shares		76,423
Accrued payroll taxes						$ 444,000
Stock-based compensation expense			$ 0	$ 0
Unrecognized compensation expense			0
Restricted Cash for Tenant Improvements
Commitments and contingencies
Restricted cash			$ 12,647,000
Subsequent Event \| City and County of San Francisco Real Property Transfer Tax Case \| Pending Litigation
Commitments and contingencies
Damages sought	$ 11,500,000