Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 01, 2019
Cover [Abstract]
Entity Registrant Name	IONIS PHARMACEUTICALS INC
Entity Central Index Key	0000874015
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		140,500,298
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	000-19125
Entity Tax Identification Number	33-0336973
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	2855 Gazelle Court
Entity Address, City or Town	Carlsbad
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92010
City Area Code	760
Local Phone Number	931-9200
Title of 12(b) Security	Common Stock, $.001 Par Value
Trading Symbol	IONS
Security Exchange Name	NASDAQ