XML 76 R62.htm IDEA: XBRL DOCUMENT
v3.22.4

Borrowings - SBA-guaranteed Debentures, Narrative (Details) $ in Thousands | 12 Months Ended |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
SBA-guaranteed debentures outstanding | $ 300,000 | $ 300,000 | $ 300,000 | $ 225,000 | $ 165,000 | $ 150,000 | $ 121,700 | $ 117,700 | $ 37,500
Upfront fees percentage | 0.03435 |  |  |  |  |  |  |  |
Commitment fee percentage | 0.0100 |  |  |  |  |  |  |  |
Issuance discount percentage | 0.02435 |  |  |  |  |  |  |  |
SBIC I |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Regulatory capital | $ 75,000 | 75,000 |  |  |  |  |  |  |
SBA-guaranteed debentures outstanding | 150,000 | 150,000 |  |  |  |  |  |  |
SBIC II |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Regulatory capital | 75,000 | 75,000 |  |  |  |  |  |  |
SBA-guaranteed debentures outstanding | $ 150,000 | $ 150,000 |  |  |  |  |  |  |
SBA-guaranteed debentures |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Term of debt | 10 years |  |  |  |  |  |  |  |
SBA-guaranteed debentures | LIBOR |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest rate margin | 0.30% |  |  |  |  |  |  |  |

X
- Definition Guaranteed Debt + References No definition available. + Details
Name: | nmfc_GuaranteedDebt
Namespace Prefix: | nmfc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Guaranteed Debt, Commitment Fee + References No definition available. + Details
Name: | nmfc_GuaranteedDebtCommitmentFee
Namespace Prefix: | nmfc_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Guaranteed Debt, Issuance Discount + References No definition available. + Details
Name: | nmfc_GuaranteedDebtIssuanceDiscount
Namespace Prefix: | nmfc_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Guaranteed Debt, Upfront Fees + References No definition available. + Details
Name: | nmfc_GuaranteedDebtUpfrontFees
Namespace Prefix: | nmfc_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Small Business Association Regulation, Regulatory Capital, Actual + References No definition available. + Details
Name: | nmfc_SmallBusinessAssociationRegulationRegulatoryCapitalActual
Namespace Prefix: | nmfc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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 No definition available. + Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=nmfc_NewMountainFinanceSBICLPMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=nmfc_NewMountainFinanceSBICIILPMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=nmfc_GuaranteedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |