| Document and Entity Information | Dec. 11, 2019 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001426800 |
| Document Type | 8-K |
| Document Period End Date | Dec. 11, 2019 |
| Entity Registrant Name | Assembly Biosciences, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-35005 |
| Entity Tax Identification Number | 20-8729264 |
| Entity Address, Address Line One | 11711 N. Meridian St. |
| Entity Address, Address Line Two | Suite 310 |
| Entity Address, City or Town | Carmel |
| Entity Address, State or Province | IN |
| Entity Address, Postal Zip Code | 46032 |
| City Area Code | (833) |
| Local Phone Number | 509-4583 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.001 |
| Trading Symbol | ASMB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
