Debt and Foreign Currency Transactions and Translations - Additional Information (Details)						9 Months Ended	12 Months Ended
		Dec. 13, 2023 USD ($)	Apr. 19, 2023	Jul. 16, 2021 USD ($)	Mar. 03, 2015 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($) Installment		Dec. 31, 2022 USD ($)		Dec. 23, 2024 USD ($)	Dec. 22, 2024 USD ($)	Nov. 02, 2023 USD ($)	Nov. 19, 2022 USD ($)	Apr. 04, 2019	Apr. 04, 2018
Debt Instrument [Line Items]
Aggregate principal amount						$ 2,238,829,000	$ 2,492,000,000		$ 2,238,829,000
Debt						1,483,394,000	1,462,267,000		$ 1,483,394,000
MFIC Bethesda CLO 1 LLC Debt Securitization Member
Debt Instrument [Line Items]
Debt							402,360,000
Subordinated Debt	[1]						$ 154,360,000
Term debt securitization													$ 402,360,000
Senior Secured Facility
Debt Instrument [Line Items]
Required assets coverage percentage															150.00%	200.00%
Final Maturity Date							Apr. 19, 2028	[2]	Dec. 22, 2025	[3]
Credit facility expiration date			Apr. 19, 2028
Aggregate principal amount						1,763,829,000	$ 1,705,000,000		$ 1,763,829,000
Date of first required payment to repay							Apr. 19, 2027
Number of installment | Installment							12
Frequency of payment and payment terms							Commencing April 19, 2027, the Company is required to repay, in twelve consecutive monthly installments of equal size, the outstanding amount under the Senior Secured Facility as of April 19, 2027.
Frequency of periodic payment							monthly
Commitment fee per annum							0.375%
Required minimum percentage of equity to assets							30.00%
Base amount considered for covenants							$ 705,000,000
Considered percentage of net proceeds from sale of equity interest for covenants							25.00%
Maximum borrowing capacity						1,763,829,000	$ 1,705,000,000		1,763,829,000					$ 1,810,000,000
Maximum borrowing capacity under accordian feature							2,325,000,000
Available remaining capacity						713,634,000	$ 1,004,732,000		$ 713,634,000
Senior Secured Facility | Forecast
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 1,550,000,000	$ 1,705,000,000
2025 Notes
Debt Instrument [Line Items]
Final Maturity Date					Mar. 03, 2025		Mar. 03, 2025	[4]	Mar. 03, 2025	[5]
Aggregate principal amount					$ 350,000,000	$ 350,000,000	$ 350,000,000		$ 350,000,000
Date of first required payment to repay					Sep. 03, 2015
Frequency of payment and payment terms						The 2025 Notes will mature on March 3, 2025. Interest on the 2025 Notes is due semi-annually on March 3 and September 3, at an annual rate of 5.25%, commencing on September 3, 2015.
Frequency of periodic payment					semi-annually
Net proceeds from senior unsecured notes					$ 343,650,000
Annual interest rate					5.25%
2026 Notes
Debt Instrument [Line Items]
Final Maturity Date				Jul. 16, 2026			Jul. 16, 2026	[4]	Jul. 16, 2026	[5]
Aggregate principal amount				$ 125,000,000		$ 125,000,000	$ 125,000,000		$ 125,000,000
Date of first required payment to repay				Jan. 16, 2022
Frequency of payment and payment terms						The 2026 Notes will mature on July 16, 2026. Interest on the 2026 Notes is due semi-annually on January 16 and July 16, at an annual rate of 4.50%, commencing on January 16, 2022.
Frequency of periodic payment				semi-annually
Net proceeds from senior unsecured notes				$ 122,965,000
Annual interest rate				4.50%
2028 Notes
Debt Instrument [Line Items]
Final Maturity Date		Dec. 15, 2028					Dec. 15, 2028	[6]
Aggregate principal amount		$ 80,000,000					$ 80,000,000
Frequency of payment and payment terms						The 2028 Notes will mature on December 15, 2028. The 2028 Notes bear interest at a rate of 8.00% per year, commencing December 13, 2023.
Annual interest rate		8.00%
Redemption period, start date		Dec. 15, 2025
Debt instrument redemption rate per note		$ 25,000
Debt instrument redemption start date		Dec. 15, 2025
2028 Notes | Over-allotment Option
Debt Instrument [Line Items]
Aggregate principal amount		$ 5,000,000
Maximum | Senior Secured Facility
Debt Instrument [Line Items]
Fronting fees on letters of credit issued							2.25%
Maximum | Senior Secured Facility | SOFR
Debt Instrument [Line Items]
Borrowing base interest rate							1.975%
Maximum | Senior Secured Facility | Alternate Base Rate
Debt Instrument [Line Items]
Borrowing base interest rate							0.875%
Minimum | Senior Secured Facility
Debt Instrument [Line Items]
Required indebtedness ratio for covenants							1.5
Minimum | Senior Secured Facility | SOFR
Debt Instrument [Line Items]
Borrowing base interest rate							1.85%
Minimum | Senior Secured Facility | Alternate Base Rate
Debt Instrument [Line Items]
Borrowing base interest rate							0.75%
Standby Letters of Credit | Senior Secured Facility
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 150,000,000
Line of credit						$ 37,692,000	$ 17,291,000		$ 37,692,000

[1] The Company retained (in the Bethesda CLO 1 Depositor) all of the Class A-2 Notes and the Subordinated Notes issued in the Bethesda CLO 1 Debt Securitization which are eliminated in consolidation.

[2] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of December 31, 2023. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.

[3] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of December 31, 2022. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.

[4] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of December 31, 2023. The valuation is based on broker quoted prices.

[5] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of December 31, 2022. The valuation is based on broker quoted prices.

[6] The fair value of these debt obligations would be categorized as Level 1 under ASC 820 as of December 31, 2023. The valuation is arrived using the closing price on exchange as on the relevant date.