| Document and Entity Information | Oct. 27, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001492422 |
| Document Type | 8-K |
| Document Period End Date | Oct. 27, 2020 |
| Entity Registrant Name | Apellis Pharmaceuticals, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-38276 |
| Entity Tax Identification Number | 27-1537290 |
| Entity Address, Address Line One | 100 Fifth Avenue |
| Entity Address, City or Town | Waltham |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02451 |
| City Area Code | (617) |
| Local Phone Number | 977-5700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock |
| Trading Symbol | APLS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
