Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(11))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

Name:	us-gaap_Assets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total costs of sales and operating expenses for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

Name:	us-gaap_CostsAndExpenses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

Name:	srt_ProductOrServiceAxis=ions_TEGSEDIProductSalesMember
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:	srt_ProductOrServiceAxis=ions_ResearchAndDevelopmentRevenueUnderCollaborativeAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=ions_AkceaTherapeuticsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ions_IonisCoreMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ions_AkceaTherapeuticsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_IntersegmentEliminationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
Segment Information (Details) $ in Thousands	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018 USD ($)	Mar. 31, 2019	Dec. 31, 2018 USD ($)	Apr. 30, 2018	Jul. 31, 2017	Jun. 30, 2017
Segment Information [Abstract]
Number of reportable segments \| Segment			2
Segment Information [Abstract]
Revenue	$ 163,813	$ 117,747	$ 461,026	$ 262,165
Total operating expenses	182,640	168,028	358,320	315,748
Income (loss) from operations	(18,827)	(50,281)	102,706	(53,583)
Total assets as of current period	2,877,765		2,877,765			$ 2,667,784
Commercial Revenue [Member]
Segment Information [Abstract]
Revenue	88,299	57,198	156,386	99,221
SPINRAZA Royalties [Member]
Segment Information [Abstract]
Revenue	70,502	56,653	130,212	97,734
TEGSEDI Product Sales, Net [Member]
Segment Information [Abstract]
Revenue	9,865	0	16,619	0
Licensing and Other Royalties [Member]
Segment Information [Abstract]
Revenue	7,932	545	9,555	1,487
R&D Revenue Under Collaborative Agreements [Member]
Segment Information [Abstract]
Revenue	$ 75,514	60,549	$ 304,640	162,944
Akcea [Member]
Segment Information [Abstract]
Percentage ownership	76.00%		76.00%		76.00%	75.00%	68.00%	68.00%	100.00%
Operating Segments [Member] \| Ionis Core [Member]
Segment Information [Abstract]
Revenue	$ 140,189	99,426	$ 362,078	231,965
Total operating expenses	121,774	85,875	236,290	191,419
Income (loss) from operations	18,415	13,551	125,788	40,546
Total assets as of current period	3,173,752		3,173,752			$ 2,975,491
Operating Segments [Member] \| Ionis Core [Member] \| Commercial Revenue [Member]
Segment Information [Abstract]
Revenue	75,398	57,198	136,731	99,221
Operating Segments [Member] \| Ionis Core [Member] \| SPINRAZA Royalties [Member]
Segment Information [Abstract]
Revenue	70,502	56,653	130,212	97,734
Operating Segments [Member] \| Ionis Core [Member] \| TEGSEDI Product Sales, Net [Member]
Segment Information [Abstract]
Revenue	0		0
Operating Segments [Member] \| Ionis Core [Member] \| Licensing and Other Royalties [Member]
Segment Information [Abstract]
Revenue	4,896	545	6,519	1,487
Operating Segments [Member] \| Ionis Core [Member] \| R&D Revenue Under Collaborative Agreements [Member]
Segment Information [Abstract]
Revenue	64,791	42,228	225,347	132,744
Operating Segments [Member] \| Akcea Therapeutics [Member]
Segment Information [Abstract]
Revenue	26,624	18,321	190,440	35,429
Total operating expenses	65,328	81,744	202,938	129,179
Income (loss) from operations	(38,704)	(63,423)	(12,498)	(93,750)
Total assets as of current period	434,120		434,120			365,261
Operating Segments [Member] \| Akcea Therapeutics [Member] \| Commercial Revenue [Member]
Segment Information [Abstract]
Revenue	15,901	0	22,655	0
Operating Segments [Member] \| Akcea Therapeutics [Member] \| SPINRAZA Royalties [Member]
Segment Information [Abstract]
Revenue	0	0	0	0
Operating Segments [Member] \| Akcea Therapeutics [Member] \| TEGSEDI Product Sales, Net [Member]
Segment Information [Abstract]
Revenue	9,865		16,619
Operating Segments [Member] \| Akcea Therapeutics [Member] \| Licensing and Other Royalties [Member]
Segment Information [Abstract]
Revenue	6,036	0	6,036	0
Operating Segments [Member] \| Akcea Therapeutics [Member] \| R&D Revenue Under Collaborative Agreements [Member]
Segment Information [Abstract]
Revenue	10,723	18,321	167,785	35,429
Elimination of Intercompany Activity [Member]
Segment Information [Abstract]
Revenue	(3,000)	0	(91,492)	(5,229)
Total operating expenses	(4,462)	409	(80,908)	(4,850)
Income (loss) from operations	1,462	(409)	(10,584)	(379)
Total assets as of current period	(730,107)		(730,107)			$ (672,968)
Elimination of Intercompany Activity [Member] \| Commercial Revenue [Member]
Segment Information [Abstract]
Revenue	(3,000)	0	(3,000)	0
Elimination of Intercompany Activity [Member] \| SPINRAZA Royalties [Member]
Segment Information [Abstract]
Revenue	0	0	0	0
Elimination of Intercompany Activity [Member] \| TEGSEDI Product Sales, Net [Member]
Segment Information [Abstract]
Revenue	0		0
Elimination of Intercompany Activity [Member] \| Licensing and Other Royalties [Member]
Segment Information [Abstract]
Revenue	(3,000)	0	(3,000)	0
Elimination of Intercompany Activity [Member] \| R&D Revenue Under Collaborative Agreements [Member]
Segment Information [Abstract]
Revenue	$ 0	$ 0	$ (88,492)	$ (5,229)