Sale Of Stock, Maximum Issuance, Amount

No definition available.

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Namespace Prefix:	nmfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Sale Of Stock, Remaining Stock Available For Issuance, Amount

+ References

No definition available.

+ Details

Name:	nmfc_SaleOfStockRemainingStockAvailableForIssuanceAmount
Namespace Prefix:	nmfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap-supplement_InvestmentCompanyChangesInNetAssetsLineItems
Namespace Prefix:	us-gaap-supplement_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow for cost incurred directly with the issuance of an equity security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3291-108585

+ Details

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

- Definition

Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

+ Details

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

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=nmfc_AtTheMarketOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Net Assets - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
Net Assets - Narrative (Details) - USD ($) $ in Thousands	Nov. 03, 2021	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2021
Investment Company, Changes in Net Assets [Line Items]
Offering expenses			$ 132	$ 0
Sale of stock, remaining amount available for issuance and sale		$ 196,938	$ 196,938
ATM Offering
Investment Company, Changes in Net Assets [Line Items]
Sale of stock, issuance amount	$ 250,000
Sale of stock, number of shares issued (in shares)		220,098	2,950,300
Sale of stock, consideration received		$ 2,956	$ 40,007
Offering expenses		$ 12	$ 439