Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 01, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	FLGT
Entity Registrant Name	FULGENT GENETICS, INC.
Entity Central Index Key	0001674930
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		21,697,884
Entity File Number	001-37894
Entity Tax Identification Number	81-2621304
Entity Address, Address Line One	4978 Santa Anita Avenue
Entity Address, Address Line Two	Suite 205
Entity Address, City or Town	Temple City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91780
City Area Code	626
Local Phone Number	350-0537
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE