| Document And Entity Information | Jul. 18, 2024 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Cassava Sciences, Inc. |
| Document, Type | 8-K |
| Document, Period End Date | Jul. 18, 2024 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 001-41905 |
| Entity, Tax Identification Number | 91-1911336 |
| Entity, Address, Address Line One | 6801 N Capital of Texas Highway |
| Entity, Address, Address Line Two | Building 1; Suite 300 |
| Entity, Address, City or Town | Austin |
| Entity, Address, State or Province | TX |
| Entity, Address, Postal Zip Code | 78731 |
| City Area Code | 512 |
| Local Phone Number | 501-2444 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001069530 |
| CommonStock0001ParValue Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.001 par value |
| Trading Symbol | SAVA |
| Security Exchange Name | NASDAQ |
| WarrantsExercisableForSharesOfCommonStock Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Warrants, exercisable for shares of Common Stock* |
| Trading Symbol | SAVAW |
| Security Exchange Name | NASDAQ |
