Other Obligations, Research and Development and Manufacturing Facilities (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
Jul. 31, 2017	Sep. 30, 2018
Primary R&D Facility [Member]
Research and Development and Manufacturing Facilities [Abstract]
Payment to acquire building	$ 79.4
Proceeds from mortgage loan	$ 51.3
Interest rate	3.88%
Period to make interest only payments on mortgage loan		5 years
Manufacturing Facility [Member]
Research and Development and Manufacturing Facilities [Abstract]
Payment to acquire building	$ 14.0
Proceeds from mortgage loan	$ 9.1
Interest rate	4.20%
Period to make interest only payments on mortgage loan		5 years

Period of time to make only payments of interest on the mortgage loan, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

+ Details

Name:	ions_PeriodToMakeInterestOnlyPaymentsOnMortgageLoan
Namespace Prefix:	ions_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The cash outflow for acquisition of buildings (properties) whether for investment or use.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Cash inflow associated with loan origination (the process when securing a mortgage for a piece of real property) or lease origination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ions_PrimaryResearchAndDevelopmentFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ManufacturingFacilityMember
Namespace Prefix:
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Balance Type:
Period Type: