v3.19.1
Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Mar. 15, 2019
Jun. 30, 2018
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, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Current Reporting Status Yes    
Entity Filer Category Accelerated Filer    
Entity Voluntary Filers No    
Entity Well-known Seasoned Issuer No    
Entity Small Business true    
Entity Emerging Growth Company true    
Entity Shell Company false    
Entity Ex Transition Period true    
Entity Common Stock, Shares Outstanding   41,269,643  
Entity Public Float     $ 528.2