v3.19.3
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 01, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Entity Registrant Name ACHILLION PHARMACEUTICALS INC  
Entity Central Index Key 0001070336  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   140,046,647
Entity Shell Company false  
Entity Small Business true  
Entity Emerging Growth Company false  
Title of 12(b) Security Common Stock, Par Value $0.001 per share  
Trading Symbol ACHN  
Security Exchange Name NASDAQ  
Entity File Number 001-33095  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 52-2113479  
Entity Address, Address Line One 1777 Sentry Parkway West  
Entity Address, Address Line Two Building 14, Suite 200  
Entity Address, City or Town Blue Bell  
Entity Address, State or Province PA  
Entity Address, Postal Zip Code 19422  
City Area Code 215  
Local Phone Number 709-3040  
Document Quarterly Report true  
Document Transition Report false