| Document and Entity Information | Jun. 03, 2021 |
| Document and Entity Information | |
| Document Type | 8-K |
| Document Period End Date | Jun. 3, 2021 |
| Entity File Number | 001-37581 |
| Entity Registrant Name | Aclaris Therapeutics, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 46-0571712 |
| Entity Address, Address Line One | 640 Lee Road |
| Entity Address, Adress Line Two | Suite 200 |
| Entity Address, City or Town | Wayne |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19087 |
| City Area Code | 484 |
| Local Phone Number | 324-7933 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.00001 par value |
| Trading Symbol | ACRS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001557746 |
| Amendment Flag | false |
