Main Street Capital Corporation Quarterly report pursuant to Section 13 or 15(d)

DEBT - Summary of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Jan. 31, 2021	Apr. 30, 2019	Nov. 30, 2017
Debt Instrument [Line Items]
Total Interest Expense	$ 21,234	$ 14,711	$ 55,216	$ 42,914
3.00% Notes due 2026
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.00%		3.00%
3.00% Notes due 2026 \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	$ 3,882	2,487	$ 11,645	7,124
Debt instrument, interest rate, stated percentage	3.00%		3.00%		3.00%	3.00%
5.20% Notes due 2024 \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	$ 5,714	5,714	$ 17,141	17,141
Debt instrument, interest rate, stated percentage	5.20%		5.20%		5.20%		5.20%
SBIC Debentures \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	$ 2,855	2,704	$ 8,482	8,002
4.50% Notes due 2022 \| Unsecured Notes
Debt Instrument [Line Items]
Total Interest Expense	$ 2,233	2,233	$ 6,699	6,699
Debt instrument, interest rate, stated percentage	4.50%		4.50%		4.50%			4.50%
Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Total Interest Expense	$ 6,551	$ 1,574	$ 11,249	$ 3,948