| Document and Entity Information | Nov. 04, 2021 |
| Cover [Abstract] | |
| Entity Address, Country | CA |
| Amendment Flag | false |
| Entity Central Index Key | 0000882361 |
| Document Type | 8-K |
| Document Period End Date | Nov. 4, 2021 |
| Entity Registrant Name | Aptose Biosciences Inc. |
| Entity Incorporation State Country Code | Z4 |
| Entity File Number | 001-32001 |
| Entity Tax Identification Number | 98-1136802 |
| Entity Address, Address Line One | 251 Consumers Road |
| Entity Address, Address Line Two | Suite 1105 |
| Entity Address, City or Town | Toronto |
| Entity Address, State or Province | ON |
| Entity Address, Postal Zip Code | M2J 4R3 |
| City Area Code | (647) |
| Local Phone Number | 479-9828 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Security 12b Title | Common Shares, no par value |
| Trading Symbol | APTO |
| Security Exchange Name | NASDAQ |
