Debt and Foreign Currency Transactions and Translations - Summarizes Average and Maximum Debt Outstanding and Interest and Debt Issuance Cost (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Debt Instrument [Line Items]
Average debt outstanding (in millions)		$ 1,925,540	$ 1,439,084	$ 1,866,897	$ 1,404,912
Maximum amount of debt outstanding	[1]	$ 2,053,954	$ 1,511,548	$ 2,325,684	$ 1,511,548
Weighted average annualized interest cost	[2]	6.45%	7.05%	6.42%	7.05%
Annualized amortized debt issuance cost		0.36%	0.44%	0.38%	0.50%
Total annualized interest cost		6.81%	7.49%	6.80%	7.55%

[1] The maximum amount of debt outstanding during the six months ended June 30, 2025 is inclusive of $399 million of Class A1, Class A2, Class B, and Class C Notes of MFIC Bethesda CLO 2 that were sold on February 24, 2025. The Company used the proceeds received to repay borrowings under its Senior Secured Facility on February 25, 2025, the day following the closing of MFIC Bethesda CLO 2.

[2] Includes the stated interest expense and commitment fees on the unused portion of the Senior Secured Facility. Commitment fees for the three and six months ended June 30, 2025 were $532 and $1,164, respectively. Commitment fees for the three and six months ended June 30, 2024 were $958 and $1,997, respectively.