COMMERCIAL MORTGAGE LOANS HELD-FOR-INVESTMENT - Summary of Commercial Loan Risk Ratings (Details)	6 Months Ended
	Jun. 30, 2018 USD ($) mortgage_loan	Dec. 31, 2017 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Commercial mortgage loans held-for-investment, at amortized cost	$ 326,883,547	$ 0
Commercial real estate portfolio segment
Financing Receivable, Recorded Investment [Line Items]
Number of Loans | mortgage_loan	22
Outstanding Face Amount	$ 326,883,547	0
Commercial mortgage loans held-for-investment, at amortized cost	$ 326,883,547	$ 0
Commercial real estate portfolio segment | Risk rating, 1
Financing Receivable, Recorded Investment [Line Items]
Number of Loans | mortgage_loan	0
Outstanding Face Amount	$ 0
Commercial mortgage loans held-for-investment, at amortized cost	$ 0
Commercial real estate portfolio segment | Risk rating, 2
Financing Receivable, Recorded Investment [Line Items]
Number of Loans | mortgage_loan	6
Outstanding Face Amount	$ 82,883,245
Commercial mortgage loans held-for-investment, at amortized cost	$ 82,883,245
Commercial real estate portfolio segment | Risk rating, 3
Financing Receivable, Recorded Investment [Line Items]
Number of Loans | mortgage_loan	13
Outstanding Face Amount	$ 195,210,492
Commercial mortgage loans held-for-investment, at amortized cost	$ 195,210,492
Average risk rating, percentage	85.10%
Commercial real estate portfolio segment | Risk rating, 4
Financing Receivable, Recorded Investment [Line Items]
Number of Loans | mortgage_loan	3
Outstanding Face Amount	$ 48,789,810
Commercial mortgage loans held-for-investment, at amortized cost	$ 48,789,810
Commercial real estate portfolio segment | Risk rating, 5
Financing Receivable, Recorded Investment [Line Items]
Number of Loans | mortgage_loan	0
Outstanding Face Amount	$ 0
Commercial mortgage loans held-for-investment, at amortized cost	$ 0