Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2022
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On October 27, 2022, the Company entered into a private placement purchase agreement with several purchasers, each of whom is an “accredited investor” as defined in Rule 501(a) of Regulation D under the Securities Act of 1933, as amended (the “Securities Act”) or a “qualified institutional buyer” within the meaning of Rule 144A promulgated under the Securities Act (the “Purchasers”), for the sale of $200,000 in aggregate principal amount of the Company's 7.50% convertible notes due 2025 (the “2022 Convertible Notes”). Oppenheimer & Co. Inc. acted as a placement agent for the offering. Subject to the terms and conditions of an indenture, dated as of August 20, 2018, as supplemented by a third supplemental indenture dated as of November 2, 2022 (together, the “2018C Indenture”), between the Company and U.S. Bank Trust Company, National Association (as successor in interest to U.S. Bank National Association) governing the 2022 Convertible Notes that was entered into in connection with the closing of the offering, the 2022 Convertible Notes are convertible into shares of the Company’s common stock (together with cash in lieu of fractional shares) at an initial conversion rate of 70.4225 shares of the Company’s common stock per $1,000 principal amount of 2022 Convertible Notes (subject to adjustments by the Company as provided in the 2018C Indenture), which is equal to a conversion price of approximately $14.20 per share of the Company's common stock. The conversion rate and conversion price will be subject to adjustment upon the occurrence of certain events. A holder may convert its 2022 Convertible Notes in whole or in part any time prior to the close of business on the scheduled business day immediately preceding the maturity date of October 15, 2025. The 2022 Convertible Notes will accrue interest at an annual rate of 7.50%, payable semi-annually in arrears on April 15 and October 15 of each year, commencing on April 15, 2023. The Company will use the net proceeds from the 2022 Convertible Notes to launch a tender offer for its existing 2018 Convertible Notes and then, to the extent any net proceeds remain, to repay other outstanding indebtedness and for general corporate purposes. On November 2, 2022, the Company’s board of directors declared a fourth quarter 2022 distribution of $0.32 per share payable on December 30, 2022 to holders of record as of December 16, 2022. On November 4, 2022, the Company launched a tender offer to purchase, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated November 4, 2022, up to $201,250 aggregate principal amount of outstanding 2018 Convertible Notes for cash in an amount equal to $1,000 per $1,000 principal amount of Notes purchased (exclusive of accrued and unpaid interest on such notes) (the "Tender Offer"). The Tender Offer will expire at 11:59 P.M., New York City time, on December 6, 2022. On November 7, 2022, the Company’s board of directors appointed John R. Kline as the Chief Executive Officer of the Company, effective January 1, 2023, in addition to continuing in his role as President and a director. Mr. Kline joined New Mountain in 2008 and has been a senior executive within New Mountain Capital's credit effort since its inception that year. Also on November 7, 2022, the Company’s board of directors received and accepted the resignation of Robert A. Hamwee as Chief Executive Officer and appointed him Vice Chairman of the board of directors, effective January 1, 2023, with the continued ability to allocate half of his time to activities outside of credit and NMFC. As part of his responsibilities, Mr. Hamwee will continue to: (i) serve as a director of the Company and (ii) serve as a senior member of the Investment Committee of the Company’s Investment Adviser. The Company’s Investment Adviser believes that its management team, with the overall support of New Mountain Capital’s team of 215 professionals, is adequately staffed to support the Company.