The number of agreements entered into with the collaboration partner.

No definition available.

Name:	ions_NumberOfAgreementsWithCollaborationPartner
Namespace Prefix:	ions_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of performance obligations at the inception of a contract.

+ References

No definition available.

+ Details

Name:	ions_RevenueFromContractWithCustomerNumberOfPerformanceObligationsAtInceptionOfContract
Namespace Prefix:	ions_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of separate performance obligations under the collaboration agreement.

+ References

No definition available.

+ Details

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

- Definition

The amount of consideration the Company earned or is eligible to earn under the collaboration agreement, including any variable consideration.

+ References

No definition available.

+ Details

Name:	ions_RevenueFromContractWithCustomerTransactionPrice
Namespace Prefix:	ions_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The additional amount of consideration the Company earned under the collaboration agreement that is added to the transaction price.

+ References

No definition available.

+ Details

Name:	ions_RevenueFromContractWithCustomerTransactionPriceAdditions
Namespace Prefix:	ions_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of upfront payments received during the period under the collaboration agreement.

+ References

No definition available.

+ Details

Name:	ions_UpfrontPaymentReceived
Namespace Prefix:	ions_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

+ Details

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

- Details

Name:	srt_MajorCustomersAxis=ions_BiogenIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ions_LicensingAndOtherRoyaltiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementAndLicensingAgreementEnteredIntoInApril2013WithRocheMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ions_HttMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementAndLicensingAgreementEnteredIntoInOctober2018WithRocheMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementAndLicensingAgreementEnteredIntoInDecember2012WithBiogenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementAndLicensingAgreementEnteredIntoInJanuary2017WithNovartisMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementsAndLicensingAgreementsBayerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementAndLicensingAgreementEnteredIntoInMay2015WithBayerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ions_CollaborativeArrangementAndLicensingAgreementAmendedInFebruary2017WithBayerMember
Namespace Prefix:
Data Type:	na
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Period Type:

Significant Accounting Policies, Revenue Recognition (Details) $ in Thousands	1 Months Ended		3 Months Ended					12 Months Ended
	Feb. 28, 2017 USD ($) PerformanceObligation	May 31, 2015 USD ($)	Mar. 31, 2019 USD ($) PerformanceObligation	Dec. 31, 2018 USD ($)	Jun. 30, 2018 Agreement	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)
Revenue Recognition [Abstract]
Number of performance obligations at inception of contract \| PerformanceObligation			1
Revenue			$ 297,214			$ 144,419
Biogen [Member]
Revenue Recognition [Abstract]
Number of agreements \| Agreement					2
Licensing and Other Royalty Revenue [Member]
Revenue Recognition [Abstract]
Revenue			1,623			$ 942
Roche [Member] \| IONIS-HTT [Member]
Revenue Recognition [Abstract]
Revenue			35,000					$ 0
IONIS-FB-L for Complement-Mediated Diseases [Member]
Revenue Recognition [Abstract]
Upfront payment received				$ 75,000
Neurology [Member]
Revenue Recognition [Abstract]
Milestone payment earned and amortized over period of performance							$ 10,000
Novartis [Member] \| Licensing and Other Royalty Revenue [Member]
Revenue Recognition [Abstract]
Revenue			$ 150,000
Bayer [Member]
Revenue Recognition [Abstract]
Number of separate performance obligations \| PerformanceObligation	3
Bayer [Member]
Revenue Recognition [Abstract]
Upfront payment received		$ 100,000
Bayer [Member]
Revenue Recognition [Abstract]
Upfront payment received	$ 75,000
Transaction price	$ 75,000