| Document And Entity Information | May 09, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 9, 2022 |
| Entity Registrant Name | ENANTA PHARMACEUTICALS, INC. |
| Entity Central Index Key | 0001177648 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-35839 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 04-3205099 |
| Entity Address, Address Line One | 500 Arsenal Street |
| Entity Address, City or Town | Watertown |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02472 |
| City Area Code | (617) |
| Local Phone Number | 607-0800 |
| Entity Information, Former Legal or Registered Name | Not Applicable |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | ENTA |
| Security Exchange Name | NASDAQ |
