v3.26.3
Investments - Selected Balance Sheet Information for SLP III and SLP IV (Details) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Investments, cost $ 2,453,990 [1] $ 2,912,115 [2]
Investments at fair value 2,259,962 [1] 2,742,013 [2]
Receivable from unsettled securities sold 0 4,138
Total assets 2,352,701 2,902,853
Deferred financing costs, accumulated amortization 50,994 45,302
Deferred financing costs (net of accumulated amortization) (15,470) (17,875)
Payable for unsettled securities purchased 168 463
Other liabilities 4,064 2,181
Total liabilities 1,338,493 1,714,597
Total liabilities and net assets 2,352,701 2,902,853
SLP III    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Investments, cost 920,103 957,232
Investments at fair value 872,188 941,427
Cash and other assets 30,661 28,469
Receivable from unsettled securities sold 30,775 0
Total assets 933,624 969,896
Deferred financing costs, accumulated amortization 8,861 7,948
Deferred financing costs (net of accumulated amortization) (3,394) (4,308)
Payable for unsettled securities purchased 15,116 105,171
Distribution payable 4,625 7,000
Other liabilities 10,300 8,462
Total liabilities 784,847 789,025
Members' capital 148,777 180,871
Total liabilities and net assets 933,624 969,896
SLP III | Revolving Credit Facility    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Credit facility 758,200 672,700
SLP IV    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Investments, cost 627,324 654,867
Investments at fair value 592,086 641,452
Cash and other assets 28,475 31,324
Receivable from unsettled securities sold 24,656 0
Total assets 645,217 672,776
Deferred financing costs, accumulated amortization 5,290 4,022
Deferred financing costs (net of accumulated amortization) (3,176) (4,444)
Payable for unsettled securities purchased 9,759 66,866
Distribution payable 3,218 4,826
Other liabilities 7,976 6,978
Total liabilities 539,914 545,963
Members' capital 105,303 126,813
Total liabilities and net assets 645,217 672,776
SLP IV | Revolving Credit Facility    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Credit facility $ 522,137 $ 471,737
[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.