v2.4.0.8
Document and Entity Information (USD $)
12 Months Ended
Dec. 31, 2013
Mar. 19, 2014
Document And Entity Information [Abstract]    
Document Type 10-K  
Amendment Flag false  
Document Period End Date Dec. 31, 2013  
Document Fiscal Year Focus 2013  
Document Fiscal Period Focus FY  
Trading Symbol FPRX  
Entity Registrant Name FIVE PRIME THERAPEUTICS INC  
Entity Central Index Key 0001175505  
Current Fiscal Year End Date --12-31  
Entity Well-known Seasoned Issuer No  
Entity Current Reporting Status Yes  
Entity Voluntary Filers No  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   21,357,363
Entity Public Float   $ 0