| Cover | Aug. 31, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 31, 2021 |
| Entity File Number | 001-36306 |
| Entity Registrant Name | Eagle Pharmaceuticals, Inc. |
| Entity Central Index Key | 0000827871 |
| Entity Tax Identification Number | 20-8179278 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 50 Tice Boulevard |
| Entity Address, Address Line Two | Suite 315 |
| Entity Address, City or Town | Woodcliff Lake |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07677 |
| City Area Code | 201 |
| Local Phone Number | 326-5300 |
| 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 $0.001 per share) |
| Trading Symbol | EGRX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
