Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 11, 2019
Document And Entity Information Abstract    
Entity Registrant Name Entasis Therapeutics Holdings Inc.  
Entity Central Index Key 0001724344  
Document Type 10-Q  
Document Period End Date Sep. 30, 2019  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Common Stock, Shares Outstanding   13,291,563
Entity Shell Company false  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3