v3.26.1
Fair Value - Schedule of Unobservable Inputs Used in the Fair Value Measurement (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 2,289,805 [1] $ 2,742,013 [2]
Level III    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 2,229,035 2,698,434
Level III | First lien | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 1,378,905 $ 1,765,624
Level III | First lien | Market & income approach | Low | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 6.0 5.0
Level III | First lien | Market & income approach | Low | Revenue multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 2.0 4.0
Level III | First lien | Market & income approach | Low | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.065 0.061
Level III | First lien | Market & income approach | High | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 22.0 31.3
Level III | First lien | Market & income approach | High | Revenue multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 10.0 19.5
Level III | First lien | Market & income approach | High | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.573 0.216
Level III | First lien | Market & income approach | Weighted Average | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 13.3 14.3
Level III | First lien | Market & income approach | Weighted Average | Revenue multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 5.9 10.3
Level III | First lien | Market & income approach | Weighted Average | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.111 0.091
Level III | First lien | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 15,269 $ 9,012
Level III | Second lien | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 72,991 $ 84,722
Level III | Second lien | Market & income approach | Low | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 10.0 14.0
Level III | Second lien | Market & income approach | Low | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.100 0.094
Level III | Second lien | Market & income approach | High | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 16.0 18.0
Level III | Second lien | Market & income approach | High | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 1.602 0.158
Level III | Second lien | Market & income approach | Weighted Average | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 13.8 16.0
Level III | Second lien | Market & income approach | Weighted Average | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.217 0.135
Level III | Second lien | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value   $ 6,457
Level III | Subordinated | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 93,755 $ 121,487
Level III | Subordinated | Market & income approach | Low | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 7.5 7.0
Level III | Subordinated | Market & income approach | Low | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.127 0.117
Level III | Subordinated | Market & income approach | High | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 20.0 20.0
Level III | Subordinated | Market & income approach | High | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.195 0.189
Level III | Subordinated | Market & income approach | Weighted Average | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 12.8 13.4
Level III | Subordinated | Market & income approach | Weighted Average | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.164 0.141
Level III | Subordinated | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 4,674  
Level III | Structured Finance Obligations | Income Approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 3,191 $ 3,277
Level III | Structured Finance Obligations | Income Approach | Low | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.111 0.105
Level III | Structured Finance Obligations | Income Approach | High | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.111 0.105
Level III | Structured Finance Obligations | Income Approach | Weighted Average | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.111 0.105
Level III | Equity and other | Market & income approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 263,639 $ 320,328
Level III | Equity and other | Market & income approach | Low | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 6.0 5.5
Level III | Equity and other | Market & income approach | Low | Revenue multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 6.5 8.5
Level III | Equity and other | Market & income approach | Low | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.089 0.093
Level III | Equity and other | Market & income approach | High | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 21.4 21.7
Level III | Equity and other | Market & income approach | High | Revenue multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 8.5 10.5
Level III | Equity and other | Market & income approach | High | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.516 0.202
Level III | Equity and other | Market & income approach | Weighted Average | EBITDA multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 11.0 11.7
Level III | Equity and other | Market & income approach | Weighted Average | Revenue multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 7.0 9.0
Level III | Equity and other | Market & income approach | Weighted Average | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.240 0.117
Level III | Equity and other | Other    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 11,799  
Level III | Equity and other | Income Approach    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 384,812 $ 387,527
Level III | Equity and other | Income Approach | Low | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.064 0.063
Level III | Equity and other | Income Approach | High | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.143 0.157
Level III | Equity and other | Income Approach | Weighted Average | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.111 0.114
[1] New Mountain Finance Corporation (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] New Mountain Finance Corporation (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.