| Cover | Nov. 09, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 9, 2021 |
| Entity File Number | 001-38535 |
| Entity Registrant Name | APTINYX INC. |
| Entity Central Index Key | 0001674365 |
| Entity Tax Identification Number | 47-4626057 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 909 Davis Street |
| Entity Address, Address Line Two | Suite 600 |
| Entity Address, City or Town | Evanston |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60201 |
| City Area Code | 847 |
| Local Phone Number | 871-0377 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value per share |
| Trading Symbol | APTX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
