Debt and Foreign Currency Transactions and Translations - Schedule of Outstanding Debt Obligations (Details) - USD ($)					6 Months Ended		12 Months Ended
		Dec. 13, 2023	Jul. 16, 2021	Mar. 03, 2015	Jun. 30, 2025		Dec. 31, 2024		Dec. 31, 2023
Debt Instrument [Line Items]
Total Aggregate Principal Amount Committed					$ 2,496,000,000		$ 2,447,000,000
Principal Amount Outstanding					2,057,946,000		1,757,148,000
Deferred Financing Costs and Debt Discount					(6,292,000)		(5,527,000)
Total Bethesda CLO 1 Notes					2,051,654,000		1,751,621,000
Fair Value of Debt Obligations					$ 2,054,977,000		$ 1,754,692,000
Senior Secured Facility
Debt Instrument [Line Items]
Date Issued/ Amended					Oct. 17, 2024		Oct. 17, 2024
Total Aggregate Principal Amount Committed					$ 1,660,000,000	[1]	$ 1,660,000,000	[2]
Principal Amount Outstanding					1,221,946,000	[3]	970,148,000	[4]
Fair Value of Debt Obligations					$ 1,221,946,000	[5]	$ 970,148,000	[6]
Final Maturity Date					Oct. 17, 2029		Oct. 17, 2029
MFIC Bethesda CLO 1 LLC Class A-1 Notes
Debt Instrument [Line Items]
Date Issued/ Amended					Nov. 02, 2023		Nov. 02, 2023
Total Aggregate Principal Amount Committed					$ 232,000,000		$ 232,000,000
Principal Amount Outstanding					232,000,000		232,000,000
Fair Value of Debt Obligations					$ 232,737,000	[7]	$ 232,812,000	[8]
Final Maturity Date					Oct. 23, 2035		Oct. 23, 2035
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
Total Aggregate Principal Amount Committed					$ 399,000,000
Principal Amount Outstanding					399,000,000
Fair Value of Debt Obligations	[7]				$ 397,490,000
Final Maturity Date					Jan. 23, 2037
2025 Notes
Debt Instrument [Line Items]
Date Issued/ Amended							Mar. 03, 2015
Total Aggregate Principal Amount Committed				$ 350,000,000			$ 350,000,000
Principal Amount Outstanding							350,000,000
Fair Value of Debt Obligations	[8]						$ 349,342,000
Final Maturity Date				Mar. 03, 2025			Mar. 03, 2025
2026 Notes
Debt Instrument [Line Items]
Date Issued/ Amended					Jul. 16, 2021		Jul. 16, 2021
Total Aggregate Principal Amount Committed			$ 125,000,000		$ 125,000,000		$ 125,000,000
Principal Amount Outstanding					125,000,000		125,000,000
Fair Value of Debt Obligations					$ 121,844,000	[7]	$ 120,918,000	[8]
Final Maturity Date			Jul. 16, 2026		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 of Debt Obligations					$ 80,960,000	[9]	$ 81,472,000	[10]
Final Maturity Date		Dec. 15, 2028			Dec. 15, 2028		Dec. 15, 2028

[1] As of June 30, 2025, total lender commitments were $1,660,000.

[2] Between October 17, 2024 and December 22, 2024, total lender commitments were $1,815,000. As of December 31, 2024, total lender commitments were $1,660,000.

[3] Includes 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 June 30, 2025. 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, 2024. 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 June 30, 2025. The valuation is based on broker quoted prices.

[8] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of December 31, 2024. 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 June 30, 2025. The valuation is arrived 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, 2024. The valuation is arrived using the closing price on exchange as on the relevant date.