| Document and Entity Information | Nov. 06, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 6, 2019 |
| Entity Registrant Name | IONIS PHARMACEUTICALS, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-19125 |
| Entity Tax Identification Number | 33-0336973 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000874015 |
| Title of 12(b) Security | Common Stock, $.001 Par Value |
| Trading Symbol | IONS |
| Security Exchange Name | NASDAQ |
