| Document and Entity Information | Aug. 01, 2022 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Aug. 01, 2022 |
| Entity File Number | 001-32295 |
| Entity Registrant Name | FENNEC PHARMACEUTICALS INC. |
| Entity Incorporation, State or Country Code | A1 |
| Entity Tax Identification Number | 20-0442384 |
| Entity Address State Or Province | NC |
| Entity Address, Address Line One | PO Box 13628 |
| Entity Address, Adress Line Two | 68 TW Alexander Drive |
| Entity Address, City or Town | Research Triangle Park |
| Entity Address, Postal Zip Code | 27709 |
| City Area Code | 919 |
| Local Phone Number | 636-4530 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common shares, no par value |
| Trading Symbol | FENC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001211583 |
| Amendment Flag | false |
