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Cover
Jun. 26, 2024
Document Information [Line Items]  
Document Type N-2ASR
Dividend or Interest Reinvestment Plan Only false
Delayed or Continuous Offering true
Effective Upon Filing, 462(e) true
Additional Securities Effective, 413(b) false
Effective when Declared, Section 8(c) false
New Effective Date for Previous Filing false
Additional Securities. 462(b) false
No Substantive Changes, 462(c) false
Exhibits Only, 462(d) false
Approximate Date of Commencement of Proposed Sale to Public From time to time after the effective date of this Registration Statement.
Amendment Flag false
Entity Information [Line Items]  
Entity Registrant Name New Mountain Finance Corporation
Entity Central Index Key 0001496099
Entity Well-known Seasoned Issuer Yes
Entity Emerging Growth Company false
Entity Inv Company Type N-2
Entity Contact Personnel [Line Items]  
Entity Address, Address Line One 1633 Broadway
Entity Address, Address Line Two 48th Floor
Entity Address, City or Town New York
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10019
Entity Phone Fax Numbers [Line Items]  
City Area Code 212
Local Phone Number 720-0300
Business Contact [Member]  
Entity Contact Personnel [Line Items]  
Contact Personnel Name John R. Kline
Entity Address, Address Line One New Mountain Finance Corporation 1633 Broadway
Entity Address, Address Line Two 48th Floor
Entity Address, City or Town New York
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10019