Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details)	Mar. 31, 2019 Company
Cash, Cash Equivalents and Investments [Abstract]
Number of publicly-held companies in which there is an equity ownership interest of less than 20%	2
Number of privately-held companies in which there is an equity ownership interest of less than 20%	4

Number of privately-held companies, in which the entity has an equity ownership interest of less than 20%, with which it conducts business. These are accounted for under the cost method.

No definition available.

Name:	ions_NumberOfPrivatelyHeldCompaniesInWhichEntityHasEquityInvestment
Namespace Prefix:	ions_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant