Sale Of Stock, Maximum Issuance, Amount

No definition available.

Name:	nmfc_SaleOfStockMaximumIssuanceAmount
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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477796/946-210-45-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 205
-Name Accounting Standards Codification
-Section 45
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478009/946-205-45-4

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-1

+ Details

Name:	us-gaap_InvestmentCompanyChangesInNetAssetsLineItems
Namespace Prefix:	us-gaap_
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
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-15

+ 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		6 Months Ended
Net Assets - Narrative (Details) - USD ($) $ in Thousands	Jun. 27, 2024	May 18, 2023	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Investment Company, Changes in Net Assets [Line Items]
Offering expenses					$ 75	$ 178
Sale of stock, remaining amount available for issuance and sale			$ 257,991		$ 257,991
ATM Offering
Investment Company, Changes in Net Assets [Line Items]
Sale of stock, issuance amount	$ 400,000	$ 250,000
Sale of stock, number of shares issued (in shares)			0	1,562,122	0	5,292,556
Sale of stock, proceeds received				$ 19,772		$ 67,691
Offering expenses				$ 5		$ 12