| Cover | Jul. 25, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 25, 2024 |
| Entity Registrant Name | Main Street Capital Corporation |
| Entity Incorporation, State or Country Code | MD |
| Securities Act File Number | 001-33723 |
| Entity Tax Identification Number | 41-2230745 |
| Entity Address, Address Line One | 1300 Post Oak Boulevard |
| Entity Address, Address Line Two | 8th Floor |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77056 |
| City Area Code | 713 |
| Local Phone Number | 350-6000 |
| Written Communications | false |
| Soliciting Material | true |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | MAIN |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001396440 |
| Amendment Flag | false |
