Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 03, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	1-36282
Entity Registrant Name	LA JOLLA PHARMACEUTICAL COMPANY
Entity Incorporation, State or Country Code	CA
Entity Tax Identification Number	33-0361285
Entity Address, Address Line One	201 Jones Road
Entity Address, Address Line Two	Suite 400
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	617
Local Phone Number	715-3600
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	LJPC
Security Exchange Name	NASDAQ
Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Shell Company	false
Entity Common Stock, Shares Outstanding		27,448,571
Entity Central Index Key	0000920465
Document Period End Date	Mar. 31, 2021
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31