| Document and Entity Information | Oct. 14, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001832168 |
| Document Type | 8-K |
| Document Period End Date | Oct. 14, 2024 |
| Entity Registrant Name | Longboard Pharmaceuticals, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-40192 |
| Entity Tax Identification Number | 84-5009619 |
| Entity Address, Address Line One | 4275 Executive Square |
| Entity Address, Address Line Two | Suite 950 |
| Entity Address, City or Town | La Jolla |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92037 |
| City Area Code | (858) |
| Local Phone Number | 789-9283 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common stock, par value $0.0001 per share |
| Trading Symbol | LBPH |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
