Main Street Capital Corporation Annual report pursuant to Section 13 and 15(d)

Annual report pursuant to Section 13 and 15(d)

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

DEBT - Notes Due and SBIC Debentures Narrative (Details)	1 Months Ended						12 Months Ended
	Oct. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jul. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 30, 2019 USD ($)	Nov. 30, 2017 USD ($)	Dec. 31, 2023 USD ($)	Feb. 28, 2023 USD ($)	Dec. 31, 2022 USD ($) agency
Debt Instrument [Line Items]
Payable							$ 1,810,000,000		$ 2,007,000,000
Recorded value							1,802,344,000		1,999,102,000
Unsecured Notes \| July 2026 Notes
Debt Instrument [Line Items]
Debt instrument, face amount	$ 200,000,000	$ 300,000,000					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%
Payable							500,000,000		500,000,000
Recorded value							498,662,000		498,136,000
Unsecured Notes \| May 2024 Notes
Debt Instrument [Line Items]
Debt instrument, face amount			$ 125,000,000	$ 75,000,000	$ 250,000,000		450,000,000		450,000,000
Debt instrument, interest rate, stated (as a percent)					5.20%
Debt instrument, issuance price (as a percent)			102.70%	105.00%	99.125%
Payable							450,000,000		450,000,000
Recorded value							450,182,000		450,727,000
Unsecured Notes \| SBIC Debentures
Debt Instrument [Line Items]
Debt instrument, face amount							350,000,000		350,000,000
Payable							$ 350,000,000		$ 350,000,000
Debt instrument, term (in years)							10 years
Debt instrument, weighted-average annual interest rate (as a percent)							3.00%		2.90%
Debt instrument, remaining term (in years)							4 years 7 months 6 days
Recorded value							$ 344,535,000		$ 343,914,000
Unsecured Notes \| SBIC Debentures \| MSMF
Debt Instrument [Line Items]
Debt instrument, face amount							175,000,000
Recorded value							172,000,000
Unamortized debt issuance costs							3,000,000
Unsecured Notes \| SBIC Debentures \| MSC III
Debt Instrument [Line Items]
Debt instrument, face amount							175,000,000
Recorded value							172,500,000
Unamortized debt issuance costs							2,500,000
Unsecured Notes \| SBIC Debentures \| Maximum
Debt Instrument [Line Items]
Payable							350,000,000
Unsecured Notes \| December 2025 Notes
Debt Instrument [Line Items]
Debt instrument, face amount							150,000,000		100,000,000
Payable							150,000,000		100,000,000
Recorded value							$ 148,965,000		$ 99,325,000
Debt instrument, credit rating, below investment grade event, percentage of agencies (as a percent)							67.00%
Debt instrument, secured debt ratio event									0.35
Unsecured Notes \| December 2025 Notes \| Minimum
Debt Instrument [Line Items]
Debt instrument, credit rating, below investment grade rating, number of agencies \| agency									1
Unsecured Notes \| December 2025 Notes \| Maximum
Debt Instrument [Line Items]
Debt instrument, credit rating, below investment grade rating, number of agencies \| agency									2
Unsecured Notes \| December 2025 Series A Notes
Debt Instrument [Line Items]
Debt instrument, face amount									$ 100,000,000
Debt instrument, interest rate, stated (as a percent)									7.84%
Unsecured Notes \| December 2025 Series B Notes
Debt Instrument [Line Items]
Debt instrument, face amount								$ 50,000,000
Debt instrument, interest rate, stated (as a percent)								7.53%
Unsecured Notes \| December 2022 Notes
Debt Instrument [Line Items]
Debt instrument, face amount						$ 185,000,000
Debt instrument, interest rate, stated (as a percent)						4.50%
Debt instrument, issuance price (as a percent)						99.16%