Cover - USD ($)	12 Months Ended
	Dec. 31, 2020	Jun. 30, 2020	Feb. 25, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-36306
Entity Registrant Name	Eagle Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8179278
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
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	EGRX
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float		$ 514,326,120
Entity Common Stock, Shares Outstanding			13,217,284
Documents Incorporated by Reference	Portions of the definitive proxy statement for our 2021 annual meeting of stockholders, which is to be filed within 120 days after the end of the fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Form 10-K, to the extent described in Part III.
Entity Central Index Key	0000827871
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Current Fiscal Year End Date	--12-31