    <SEC-DOCUMENT>0001496099-21-000003-index.html : 20210224
    <SEC-HEADER>0001496099-21-000003.hdr.sgml : 20210224
    <ACCEPTANCE-DATETIME>20210224170124
    ACCESSION NUMBER:		0001496099-21-000003
    CONFORMED SUBMISSION TYPE:	10-K
    PUBLIC DOCUMENT COUNT:		11
    CONFORMED PERIOD OF REPORT:	20201231
    FILED AS OF DATE:		20210224
    DATE AS OF CHANGE:		20210224

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			New Mountain Finance Corp
    		CENTRAL INDEX KEY:			0001496099
    		IRS NUMBER:				272978010
    		STATE OF INCORPORATION:			DE
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		10-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	814-00832
    		FILM NUMBER:		21674556

    	BUSINESS ADDRESS:
    		STREET 1:		787 SEVENTH AVENUE, 48TH FLOOR
    		CITY:			NEW YORK
    		STATE:			NY
    		ZIP:			10019
    		BUSINESS PHONE:		(212) 720-0300

    	MAIL ADDRESS:
    		STREET 1:		787 SEVENTH AVENUE, 48TH FLOOR
    		CITY:			NEW YORK
    		STATE:			NY
    		ZIP:			10019

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	New Mountain Guardian Corp
    		DATE OF NAME CHANGE:	20100706
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>10-K
    <SEQUENCE>1
    <FILENAME>nmfc-12312020x10k.htm
    <DESCRIPTION>10-K
    <TEXT>
    Document 1 - file: nmfc-12312020x10k.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-4.9
    <SEQUENCE>2
    <FILENAME>nmfc-12312020xexhibit49.htm
    <DESCRIPTION>EX-4.9
    <TEXT>
    Document 2 - file: nmfc-12312020xexhibit49.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-23.1
    <SEQUENCE>3
    <FILENAME>nmfc-12312020xexhibit231.htm
    <DESCRIPTION>EX-23.1
    <TEXT>
    Document 3 - file: nmfc-12312020xexhibit231.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-31.1
    <SEQUENCE>4
    <FILENAME>nmfc-12312020xexhibit311.htm
    <DESCRIPTION>EX-31.1
    <TEXT>
    Document 4 - file: nmfc-12312020xexhibit311.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-31.2
    <SEQUENCE>5
    <FILENAME>nmfc-12312020xexhibit312.htm
    <DESCRIPTION>EX-31.2
    <TEXT>
    Document 5 - file: nmfc-12312020xexhibit312.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-32.1
    <SEQUENCE>6
    <FILENAME>nmfc-12312020xexhibit321.htm
    <DESCRIPTION>EX-32.1
    <TEXT>
    Document 6 - file: nmfc-12312020xexhibit321.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-32.2
    <SEQUENCE>7
    <FILENAME>nmfc-12312020xexhibit322.htm
    <DESCRIPTION>EX-32.2
    <TEXT>
    Document 7 - file: nmfc-12312020xexhibit322.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.1
    <SEQUENCE>8
    <FILENAME>nmfc-12312020xexhibit991.htm
    <DESCRIPTION>EX-99.1
    <TEXT>
    Document 8 - file: nmfc-12312020xexhibit991.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>9
    <FILENAME>chart-0342d9fa18b8475ba791a.jpg
    <DESCRIPTION>CHART
    <TEXT>
    Document 9 - file: chart-0342d9fa18b8475ba791a.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>10
    <FILENAME>deloittelogoa241a.jpg
    <DESCRIPTION>DELOITTE LOGO
    <TEXT>
    Document 10 - file: deloittelogoa241a.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>11
    <FILENAME>image_01.jpg
    <DESCRIPTION>DELOITTE LOGO
    <TEXT>
    Document 11 - file: image_01.jpg

    </DOCUMENT>
    </SEC-DOCUMENT>