| Cover | Nov. 05, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 5, 2020 |
| Entity File Number | 001-730430 |
| Entity Registrant Name | Kiniksa Pharmaceuticals, Ltd. |
| Entity Central Index Key | 0001730430 |
| Entity Tax Identification Number | 98-1327726 |
| Entity Incorporation, State or Country Code | D0 |
| Entity Address, Address Line One | Clarendon House |
| Entity Address, Address Line Two | 2 Church Street |
| Entity Address, City or Town | Hamilton |
| Entity Address, Country | BM |
| Entity Address, Postal Zip Code | HM11 |
| City Area Code | 808 |
| Local Phone Number | 451-3453 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Common Shares $0.000273235 par value |
| Trading Symbol | KNSA |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
