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Cover
Aug. 02, 2023
Cover [Abstract]  
Document Type 8-K
Document Period End Date Aug. 02, 2023
Entity Registrant Name New Mountain Finance Corporation
Entity Incorporation, State or Country Code DE
Entity File Number 814-00832
Entity Tax Identification Number 27-2978010
Entity Address, Address Line One 1633 Broadway, 48th Floor
Entity Address, City or Town New York
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10019
City Area Code 212
Local Phone Number 720-0300
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common stock, par value $0.01 per share
Trading Symbol NMFC
Security Exchange Name NASDAQ
Entity Emerging Growth Company false
Entity Central Index Key 0001496099
Amendment Flag false