The number of shares purchased in the subsidiary.

No definition available.

Name:	ions_PurchaseOfSharesInSubsidiary
Namespace Prefix:	ions_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares received from the subsidiary for the license of TEGSEDI (inotersen) and AKCEA-TTR-L to the subsidiary.

+ References

No definition available.

+ Details

Name:	ions_SharesReceivedFromSubsidiaryForLicenseOfDrugs
Namespace Prefix:	ions_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the purchase of noncontrolling interest during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_ProceedsFromIssuanceOrSaleOfEquityAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPercentageOfOwnershipAfterTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of subsidiary's or equity investee's stock owned by parent company before stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPercentageOfOwnershipBeforeTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_OwnershipAxis=ions_AkceaTherapeuticsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Basis of Presentation (Details) - Akcea [Member] - USD ($) shares in Millions, $ in Millions		1 Months Ended	3 Months Ended	7 Months Ended
	Jul. 19, 2017	Apr. 30, 2018	Mar. 31, 2017	Jul. 18, 2017	Mar. 31, 2018
Basis of Presentation [Abstract]
Percentage ownership before IPO			100.00%	100.00%
Percentage ownership after IPO	68.00%
Percentage ownership					68.00%
Subsequent Event [Member]
Basis of Presentation [Abstract]
Percentage ownership		75.00%
Shares of Akcea stock received for license of TEGSEDI and AKCEA-TTR-L (in shares)		8.0
Additional shares of Akcea stock purchased (in shares)		10.7
Additional stock purchased in Akcea		$ 200