| Document and Entity Information | May 05, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 5, 2022 |
| Entity Registrant Name | Longboard Pharmaceuticals, Inc. |
| Entity Central Index Key | 0001832168 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity File Number | 1-40192 |
| Entity Incorporation, State or Country Code | DE |
| 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 | 619 |
| Local Phone Number | 592-9775 |
| Entity Information, Former Legal or Registered Name | N/A |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Trading Symbol | LBPH |
| Title of 12(b) Security | Common stock, par value $0.0001 per share |
| Security Exchange Name | NASDAQ |
