v3.26.3
Debt and Foreign Currency Transactions and Translations - Schedule of Outstanding Debt Obligations (Details) - USD ($)
 9 Months Ended 12 Months Ended
Dec. 13, 2023
Sep. 30, 2026
Dec. 31, 2025
Dec. 31, 2023
Jul. 16, 2021
Debt Instrument [Line Items]          
Total Aggregate Principal Amount Committed   $ 2,545,000,000 $ 2,670,000,000    
Principal Amount Outstanding   1,583,000,000 2,001,048,000    
Deferred Financing Costs and Debt Discount   (5,281,000) (5,838,000)    
Fair Value   1,581,756,000 1,997,428,000    
Total Debt Obligations, net of Deferred Financing Cost and Debt Discount   $ 1,577,719,000 $ 1,995,210,000    
Senior Secured Facility          
Debt Instrument [Line Items]          
Date Issued/ Amended   Oct. 01, 2025 Oct. 01, 2025    
Total Aggregate Principal Amount Committed   $ 1,610,000,000 [1] $ 1,610,000,000 [2]    
Principal Amount Outstanding   648,000,000 [3] 941,048,000 [4]    
Fair Value   $ 648,000,000 [5] $ 941,048,000 [6]    
Final Maturity Date   Oct. 01, 2030 Oct. 01, 2030    
MFIC Bethesda CLO 1 LLC Notes (Class A-1, Class A-2, Class B and Class C)          
Debt Instrument [Line Items]          
Date Issued/ Amended   Oct. 23, 2025 Oct. 23, 2025    
Total Aggregate Principal Amount Committed   $ 456,000,000 $ 456,000,000    
Principal Amount Outstanding   456,000,000 456,000,000    
Fair Value   $ 455,001,000 [7] $ 456,000,000    
Final Maturity Date   Oct. 23, 2037 Oct. 23, 2037    
MFIC Bethesda CLO 2 LLC Notes (Class A-1, Class A-2, Class B and Class C)          
Debt Instrument [Line Items]          
Date Issued/ Amended   Feb. 24, 2025 Feb. 24, 2025    
Total Aggregate Principal Amount Committed   $ 399,000,000 $ 399,000,000    
Principal Amount Outstanding   399,000,000 399,000,000    
Fair Value   $ 398,243,000 [7] $ 396,513,000    
Final Maturity Date   Jan. 23, 2037 Jan. 23, 2037    
2026 Notes          
Debt Instrument [Line Items]          
Date Issued/ Amended     Jul. 16, 2021    
Total Aggregate Principal Amount Committed     $ 125,000,000   $ 125,000,000
Principal Amount Outstanding     125,000,000    
Fair Value [8]     $ 123,451,000    
Final Maturity Date   Jul. 16, 2026 Jul. 16, 2026    
2028 Notes          
Debt Instrument [Line Items]          
Date Issued/ Amended   Dec. 13, 2023 Dec. 13, 2023    
Total Aggregate Principal Amount Committed $ 80,000,000 $ 80,000,000 $ 80,000,000 $ 80,000,000  
Principal Amount Outstanding   80,000,000 80,000,000    
Fair Value   $ 80,512,000 [9] $ 80,416,000 [10]    
Final Maturity Date Dec. 15, 2028 Dec. 15, 2028 Dec. 15, 2028    
[1] As of September 30, 2026, total lender commitments were $1,610,000.
[2] Between January 1, 2025 and October 1, 2025, total lender commitments were $1,660,000. As of December 31, 2025, total lender commitments were $1,610,000.
[3] foreign currency debt obligations as outlined in Foreign Currency Transactions and Translations within this note to the consolidated financial statements.
[4] Includes foreign currency debt obligations as outlined in Foreign Currency Transactions and Translations within this note to the consolidated financial statements.
[5] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of September 30, 2026. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.
[6] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of December 31, 2025. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.
[7] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of September 30, 2026. The valuation is based on quoted prices.
[8] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of December 31, 2025. The valuation is based on broker quoted prices.
[9] The fair value of these debt obligations would be categorized as Level 1 under ASC 820 as of September 30, 2026. The valuation is arrived at using the closing price on exchange as on the relevant date.
[10] The fair value of these debt obligations would be categorized as Level 1 under ASC 820 as of December 31, 2025. The valuation is arrived at using the closing price on exchange as on the relevant date.