COMMERCIAL MORTGAGE LOANS HELD-FOR-INVESTMENT - Summary of Commercial Mortgage Loans (Details)	9 Months Ended	12 Months Ended
	Sep. 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	$ 559,521,552	$ 555,172,891
Commercial real estate portfolio segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	559,521,552	555,172,891
Carrying Value	$ 559,521,552	$ 555,172,891
Loan Count | mortgage_loan	45	44
Weighted average, floating rate loan, percentage	100.00%	100.00%
Weighted average coupon rate, percentage	5.80%	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	$ 559,521,552	$ 555,172,891
Outstanding senior secured loans from loan participations	6,331,093	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	$ 553,190,459	$ 550,555,503