| Document and Entity Information | Mar. 10, 2022 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001305253 |
| Document Type | 8-K |
| Document Period End Date | Mar. 10, 2022 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36183 |
| Entity Tax Identification Number | 33-0971591 |
| Entity Registrant Name | Eiger BioPharmaceuticals, Inc. |
| Entity Address, Address Line One | Eiger BioPharmaceuticals |
| Entity Address, Address Line Two | Inc. |
| Entity Address, Address Line Three | 2155 Park Blvd. |
| Entity Address, City or Town | Palo Alto |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94306 |
| City Area Code | (650) |
| Local Phone Number | 272-6138 |
| 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 | EIGR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
