| Cover | Jun. 13, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jun. 13, 2023 |
| Entity Registrant Name | CAPITAL SOUTHWEST CORPORATION |
| Entity Incorporation, State or Country Code | TX |
| Entity File Number | 814-00061 |
| Entity Tax Identification Number | 75-1072796 |
| Entity Address, Address Line One | 8333 Douglas Avenue |
| Entity Address, Address Line Two | Suite 1100 |
| Entity Address, City or Town | Dallas |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 75225 |
| City Area Code | 214 |
| Local Phone Number | 238-5700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.25 par value per share |
| Trading Symbol | CSWC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000017313 |
| Amendment Flag | false |
