| Document And Entity Information | Mar. 07, 2024 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 07, 2024 |
| Entity Registrant Name | Runway Growth Finance Corp. |
| Entity Central Index Key | 0001653384 |
| Entity Emerging Growth Company | true |
| Entity File Number | 814-01180 |
| Entity Incorporation, State or Country Code | MD |
| Entity Tax Identification Number | 47-5049745 |
| Entity Address, Address Line One | 205 N. Michigan Ave. |
| Entity Address, Address Line Two | Suite 4200 |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60601 |
| City Area Code | (312) |
| Local Phone Number | 281-6270 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Ex Transition Period | false |
| Sec 7.50 Notes Due 2027 [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 7.50% Notes due 2027 |
| Trading Symbol | RWAYL |
| Security Exchange Name | NASDAQ |
| Common Stock Par Value 0.01 Per Share [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | RWAY |
| Security Exchange Name | NASDAQ |
| Notes 8.00 Due 2027 [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 8.00% Notes due 2027 |
| Trading Symbol | RWAYZ |
| Security Exchange Name | NASDAQ |
