v3.3.1.900
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2015
Feb. 19, 2016
Jun. 30, 2015
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2015    
Document Fiscal Year Focus 2015    
Document Fiscal Period Focus FY    
Trading Symbol ACHN    
Entity Registrant Name ACHILLION PHARMACEUTICALS INC    
Entity Central Index Key 0001070336    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status No    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   136,640,019  
Entity Public Float     $ 1,014,028,559