v3.19.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2019
May 01, 2019
Document and Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Entity Registrant Name ACHILLION PHARMACEUTICALS INC  
Entity Central Index Key 0001070336  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Trading Symbol ACHN  
Entity Emerging Growth Company false  
Entity Small Business true  
Entity Common Stock, Shares Outstanding   138,725,326