v3.26.1
Fair Value - Unobservable Inputs (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 1,396,596 [1] $ 1,512,098 [2],[3]
First lien    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 1,344,659 1,462,772
Second lien    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 18,638 19,288
Subordinated    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 13,778 11,549
Equity and other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 19,521 18,489
Level III    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 1,321,348 1,397,416
Level III | First lien    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 1,271,134 1,348,090
Level III | First lien | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 1,254,834 $ 1,230,767
Level III | First lien | Market & income approach | EBITDA multiple | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.068 7.0
Level III | First lien | Market & income approach | EBITDA multiple | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 25 31.3
Level III | First lien | Market & income approach | EBITDA multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 14.6 16.7
Level III | First lien | Market & income approach | Revenue multiple | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 2 4.0
Level III | First lien | Market & income approach | Revenue multiple | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 10 19.5
Level III | First lien | Market & income approach | Revenue multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 6.3 10.1
Level III | First lien | Market & income approach | Discount rate | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.065 0.061
Level III | First lien | Market & income approach | Discount rate | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.573 0.216
Level III | First lien | Market & income approach | Discount rate | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.103 0.090
Level III | First lien | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 16,300 $ 117,323
Level III | Second lien    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 16,915 19,288
Level III | Second lien | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 10,915 $ 19,288
Level III | Second lien | Market & income approach | EBITDA multiple | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 12 14.0
Level III | Second lien | Market & income approach | EBITDA multiple | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 16 18.0
Level III | Second lien | Market & income approach | EBITDA multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 14 16.0
Level III | Second lien | Market & income approach | Discount rate | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.103 0.113
Level III | Second lien | Market & income approach | Discount rate | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.217 0.143
Level III | Second lien | Market & income approach | Discount rate | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.162 0.129
Level III | Second lien | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 6,000  
Level III | Subordinated    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 13,778 $ 11,549
Level III | Subordinated | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 12,215 $ 11,549
Level III | Subordinated | Market & income approach | EBITDA multiple | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 8.5 8.8
Level III | Subordinated | Market & income approach | EBITDA multiple | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 16.4 18.0
Level III | Subordinated | Market & income approach | EBITDA multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 13.3 12.2
Level III | Subordinated | Market & income approach | Discount rate | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.127 0.117
Level III | Subordinated | Market & income approach | Discount rate | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.146 0.146
Level III | Subordinated | Market & income approach | Discount rate | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.143 0.140
Level III | Subordinated | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 1,563  
Level III | Equity and other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 19,521 $ 18,489
Level III | Equity and other | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 15,785 $ 18,489
Level III | Equity and other | Market & income approach | EBITDA multiple | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 8.5 8.8
Level III | Equity and other | Market & income approach | EBITDA multiple | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 18 18.0
Level III | Equity and other | Market & income approach | EBITDA multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 13.2 13.5
Level III | Equity and other | Market & income approach | Revenue multiple | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.055 7.5
Level III | Equity and other | Market & income approach | Revenue multiple | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.085 10.5
Level III | Equity and other | Market & income approach | Revenue multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.07 9.0
Level III | Equity and other | Market & income approach | Discount rate | Low    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.136 0.127
Level III | Equity and other | Market & income approach | Discount rate | High    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.136 0.127
Level III | Equity and other | Market & income approach | Discount rate | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement Input 0.136 0.127
Level III | Equity and other | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 3,736  
[1] NMF SLF I, Inc. (the "Company") generally acquires its investments in private transactions exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"). These investments are generally subject to certain limitations on resale, and may be deemed to be "restricted securities" under the Securities Act.
[2] NMF SLF I, Inc. (the "Company") generally acquires its investments in private transactions exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"). These investments are generally subject to certain limitations on resale, and may be deemed to be "restricted securities" under the Securities Act.
[3] Indicates assets that the Company deems to be "non-qualifying assets" under Section 55(a) of the Investment Company Act of 1940, as amended. Qualifying assets must represent at least 70.0% of the Company's total assets at the time of acquisition of any additional non-qualifying assets. As of December 31, 2025, 3.23% of the Company's total assets are represented by investments at fair value that are considered non-qualifying assets.