Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 29, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		13,030,130
Entity Central Index Key	0000827871
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false