v3.5.0.2
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2016
Nov. 01, 2016
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q3  
Trading Symbol ACHN  
Entity Registrant Name ACHILLION PHARMACEUTICALS INC  
Entity Central Index Key 0001070336  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   136,680,888