Commitments and Contingencies - Additional Information (Details) $ in Thousands	Sep. 30, 2022 USD ($) Loan	Dec. 31, 2021 USD ($) Loan
Commitments And Contingencies Disclosure [Abstract]
Number of commercial real estate loans, remaining future funding commitment \| Loan	32	32
Commercial real estate, remaining future funding commitment \| $	$ 70,106	$ 74,518

Number of commercial real estate loans, remaining future funding commitment

No definition available.

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Namespace Prefix:	ck0001690012_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant