Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Mar. 14, 2017
Jun. 30, 2016
Document and Entity Information      
Entity Registrant Name Aclaris Therapeutics, Inc.    
Entity Central Index Key 0001557746    
Document Type 10-K    
Document Period End Date Dec. 31, 2016    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Well-known Seasoned Issuer No    
Entity Filer Category Accelerated Filer    
Entity Common Stock, Shares Outstanding   26,088,866  
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY    
Entity Public Float     $ 156.5