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

Quarterly report pursuant to Section 13 or 15(d)

DEBT - Notes??Due and SBIC Debentures (Details)

DEBT - Notes Due and SBIC Debentures (Details)		1 Months Ended					6 Months Ended
DEBT - Notes Due and SBIC Debentures (Details)	Mar. 01, 2024 USD ($)	Jun. 30, 2024 USD ($)	May 31, 2024 USD ($)	Jan. 31, 2024 USD ($)	Oct. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Feb. 28, 2023 USD ($)	Dec. 31, 2022 USD ($) agency
Debt Instrument [Line Items]
Debt instrument, payable		$ 2,211,200,000					$ 2,211,200,000		$ 1,810,000,000
Debt		2,198,068,000					2,198,068,000		1,802,344,000
July 2026 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount		500,000,000			$ 200,000,000.0	$ 300,000,000.0	500,000,000		500,000,000
Debt instrument, interest rate, stated (as a percent)						3.00%
Debt instrument, issuance price (as a percent)					101.741%	99.004%
Debt instrument, payable		500,000,000					500,000,000		500,000,000
Debt		498,925,000					498,925,000		498,662,000
March 2029 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount		350,000,000		$ 350,000,000.0			350,000,000
Debt instrument, interest rate, stated (as a percent)				6.95%
Debt instrument, issuance price (as a percent)				99.865%
Debt instrument, payable		350,000,000					350,000,000
Debt		346,642,000					346,642,000		0
June 2027 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount		$ 300,000,000.0					$ 300,000,000.0
Debt instrument, interest rate, stated (as a percent)		6.50%					6.50%
Debt instrument, issuance price (as a percent)		99.793%
Debt instrument, payable		$ 300,000,000					$ 300,000,000
Debt		297,660,000					297,660,000		0
SBIC Debentures
Debt Instrument [Line Items]
Repayments of debt							63,800,000	$ 16,000,000
SBIC Debentures \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount		286,200,000					286,200,000		350,000,000
Debt instrument, payable		$ 286,200,000					$ 286,200,000		$ 350,000,000
Debt instrument, term (in years)							10 years
Repayments of debt	$ 63,800,000
Debt instrument, weighted-average annual interest rate (as a percent)		2.80%					2.80%		3.00%
Debt instrument, remaining term (in years)							5 years 1 month 6 days
Debt		$ 280,617,000					$ 280,617,000		$ 344,535,000
SBIC Debentures \| Unsecured Notes \| Maximum
Debt Instrument [Line Items]
Debt instrument, payable		350,000,000.0					350,000,000.0
SBIC Debentures \| Unsecured Notes \| MSMF
Debt Instrument [Line Items]
Debt instrument, face amount		111,200,000					111,200,000
Debt		107,800,000					107,800,000
Debt instrument, unamortized debt issuance costs		3,400,000					3,400,000
SBIC Debentures \| Unsecured Notes \| MSC III
Debt Instrument [Line Items]
Debt instrument, face amount		175,000,000.0					175,000,000.0
Debt		172,800,000					172,800,000
Debt instrument, unamortized debt issuance costs		2,200,000					2,200,000
December 2025 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount		150,000,000					150,000,000		150,000,000
Debt instrument, payable		150,000,000					150,000,000		150,000,000
Debt		149,224,000					149,224,000		148,965,000
Debt instrument, credit rating, below investment grade event, percentage of agencies (as a percent)											67.00%
Debt instrument, secured debt ratio event											0.35
December 2025 Notes \| Unsecured Notes \| Minimum
Debt Instrument [Line Items]
Debt instrument, credit rating, below investment grade rating, number of agencies \| agency											1
December 2025 Notes \| Unsecured Notes \| Maximum
Debt Instrument [Line Items]
Debt instrument, credit rating, below investment grade rating, number of agencies \| agency											2
December 2025 Series A Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount											$ 100,000,000.0
Debt instrument, interest rate, stated (as a percent)											7.84%
December 2025 Series B Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount										$ 50,000,000.0
Debt instrument, interest rate, stated (as a percent)										7.53%
May 2024 Notes \| Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount									450,000,000
Debt instrument, interest rate, stated (as a percent)			5.20%
Debt instrument, payable									450,000,000
Repayments of debt			$ 450,000,000.0
Debt		$ 0					$ 0		$ 450,182,000