COMMERCIAL MORTGAGE LOANS HELD-FOR-INVESTMENT - Summary of Commercial Mortgage Loans (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) mortgage_loan	Dec. 31, 2018 USD ($) mortgage_loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans held-for-investment, at amortized cost	$ 599,770,362	$ 555,172,891
Commercial real estate portfolio segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	599,770,362	555,172,891
Carrying Value	$ 599,770,362	$ 555,172,891
Loan Count | mortgage_loan	47	44
Weighted average, floating rate loan, percentage	100.00%	100.00%
Weighted average coupon rate, percentage	6.50%	6.40%
Weighted average, life (in years)	3 years 9 months 18 days	4 years 1 month 6 days
Commercial mortgage loans held-for-investment, at amortized cost	$ 599,770,362	$ 555,172,891
Outstanding senior secured loans from loan participations	8,420,227	4,617,388
Commercial real estate portfolio segment | Hunt CMT
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans held-for-investment, at amortized cost	$ 591,350,135	$ 550,555,503