| Document and Entity Information | Apr. 30, 2024 |
| Cover [Abstract] | |
| Entity Registrant Name | Oaktree Specialty Lending Corp |
| Amendment Flag | false |
| Entity Central Index Key | 0001414932 |
| Document Type | 8-K |
| Document Period End Date | Apr. 30, 2024 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 814-00755 |
| Entity Tax Identification Number | 26-1219283 |
| Entity Address, Address Line One | 333 South Grand Avenue |
| Entity Address, Address Line Two | 28th Floor |
| Entity Address, City or Town | Los Angeles |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 90071 |
| City Area Code | (213) |
| Local Phone Number | 830-6300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common stock, par value $0.01 per share |
| Trading Symbol | OCSL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
