COMMERCIAL MORTGAGE LOANS HELD-FOR-INVESTMENT - Loan Portfolio Activity (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Loans Receivable Held-For-Investment, Net, Reconciliation To Cash Flow [Roll Forward]
Balance at December 31, 2017	$ 544,586,537
Purchases, net	323,416,036	$ 0
Proceeds from principal repayments	(124,493,511)	$ 0
Commercial real estate portfolio segment
Loans Receivable Held-For-Investment, Net, Reconciliation To Cash Flow [Roll Forward]
Balance at December 31, 2017	544,586,537
Purchases, net	669,080,048
Proceeds from principal repayments	$ (124,493,511)

Loans Receivable Held-For-Investment, Net, Reconciliation To Cash Flow [Roll Forward]

No definition available.

Name:	oaks_LoansReceivableHeldForInvestmentNetReconciliationToCashFlowRollForward
Namespace Prefix:	oaks_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_NotesReceivableNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow associated with purchasing loans held for investment purposes during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireLoansHeldForInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from repayments of the balance excluding interest (principal) on loans receivable and leases held for investment purposes.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromPrincipalRepaymentsOnLoansAndLeasesHeldForInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: