v2.4.0.8
Document and Entity Information (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Mar. 11, 2015
Jun. 30, 2014
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2014    
Document Fiscal Year Focus 2014    
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   25,532,719  
Entity Public Float     $ 310.0