Main Street Capital Corporation Quarterly report [Sections 13 or 15(d)]

DEBT - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Debt Instrument [Line Items]
Total Interest Expense	$ 34,043	$ 31,168
July 2026 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	3,882	3,882
June 2027 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	6,572	6,572
August 2028 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	4,916	0
March 2029 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	6,261	6,261
SBIC debentures \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	3,097	3,151
December 2025 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	0	3,031
Credit Facility \| Corporate Facility \| Line of Credit
Debt Instrument [Line Items]
Total Interest Expense	5,892	4,455
Credit Facility \| SPV Facility \| Line of Credit
Debt Instrument [Line Items]
Total Interest Expense	$ 3,423	$ 3,816