Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2017
Mar. 12, 2018
Document And Entity Information [Abstract]    
Document Type 10-K  
Amendment Flag false  
Document Period End Date Dec. 31, 2017  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus FY  
Trading Symbol APLS  
Entity Registrant Name Apellis Pharmaceuticals, Inc.  
Entity Central Index Key 0001492422  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   50,372,762
Entity Well-known Seasoned Issuer No  
Entity Voluntary Filers No  
Entity Public Float   $ 776,665,976
Entity Current Reporting Status Yes