The number of shares available for purchase under an employee stock purchase plan.

No definition available.

Name:	ions_EmployeeStockPurchasePlanSharesAvailableForPurchase
Namespace Prefix:	ions_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average sales price of shares purchased through an employee stock purchase plan.

+ References

No definition available.

+ Details

Name:	ions_EmployeeStockPurchasePlanWeightedAverageSalesPriceOfSharesPurchased
Namespace Prefix:	ions_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of executive officers terminated by the Company during the period that begins three months before and ends twelve months following a change in control of the Company when vesting will accelerate for options and RSUs outstanding as of the termination date for executive officers

+ References

No definition available.

+ Details

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

- Definition

Period of time after a change in control of the Company when vesting will accelerate for options and RSUs outstanding as of the termination date for executive officers, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

Period of time before a change in control of the Company when vesting will accelerate for options and RSUs outstanding as of the termination date for executive officers, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

Represents the holding period from the date of purchase for stock purchased under the plan.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

+ References

+ Details

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

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of additional shares authorized for issuance under share-based payment arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

+ Details

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

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

+ Details

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

- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 3: 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(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: 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(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=ions_StockOptionPlan1989Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=ions_EquityIncentivePlan2011Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=ions_EquityIncentivePlan2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=ions_NonemployeeDirectorsStockOptionPlan2002Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=ions_EmployeeStockPurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stockholders' Equity, Stock Plans (Details)	1 Months Ended	12 Months Ended
Stockholders' Equity, Stock Plans (Details)	Jun. 30, 2009 shares	Dec. 31, 2020 Officer $ / shares shares	Jun. 30, 2020 shares	Dec. 31, 2019 shares	Jun. 30, 2019 shares	May 31, 2017 shares	Jun. 30, 2015 shares	May 31, 2015 shares
Stock Options [Member]
Stock Plans [Abstract]
Number of options outstanding (in shares)		12,335,000		11,001,000
Number of options exercisable (in shares)		7,366,000
Restricted Stock Units [Member]
Stock Plans [Abstract]
Vesting period		4 years
1989 Stock Option Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)		20,000,000.0
Number of options outstanding (in shares)		30,000
Number of options exercisable (in shares)		30,000
Number of shares available for grant (in shares)		50,000
1989 Stock Option Plan [Member] \| Stock Options [Member]
Stock Plans [Abstract]
Vesting period		4 years
Award term		7 years
1989 Stock Option Plan [Member] \| Stock Options [Member] \| One Year from Date of Grant [Member]
Stock Plans [Abstract]
Vesting percentage		25.00%
Period before options are exercisable		1 year
2011 Equity Incentive Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)					23,000,000.0	16,000,000.0	11,000,000.0	5,500,000
Number of options outstanding (in shares)		11,400,000
Number of options exercisable (in shares)		6,700,000
Number of shares available for grant (in shares)		4,300,000
Number of executive officers terminated before change in control when vesting will accelerate for executive officers \| Officer		1
Period before change in control when vesting will accelerate for executive officers		3 months
Period after change in control when vesting will accelerate for executive officers		12 months
2011 Equity Incentive Plan [Member] \| Restricted Stock Units [Member]
Stock Plans [Abstract]
Vesting period		4 years
Number of awards outstanding (in shares)		2,200,000
2020 Equity Incentive Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)		2,600,000
Number of options outstanding (in shares)		10,000.00
Number of options exercisable (in shares)		0
Number of shares available for grant (in shares)		2,600,000
2020 Equity Incentive Plan [Member] \| Stock Options [Member]
Stock Plans [Abstract]
Vesting period		4 years
2002 Non-Employee Directors' Stock Option Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)			2,800,000				2,000,000.0	1,200,000
Number of options outstanding (in shares)		1,000,000.0
Number of options exercisable (in shares)		600,000
Number of shares available for grant (in shares)		800,000
2002 Non-Employee Directors' Stock Option Plan [Member] \| Stock Options [Member]
Stock Plans [Abstract]
Award term		10 years
2002 Non-Employee Directors' Stock Option Plan [Member] \| Restricted Stock Units [Member]
Stock Plans [Abstract]
Number of awards outstanding (in shares)		100,000
Employee Stock Purchase Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)		3,200,000
Number of additional shares reserved for issuance (in shares)	150,000	150,000
Maximum percentage of employee compensation used to purchase shares		10.00%
Percentage of fair market value used to determine purchase price of stock		85.00%
Holding period for purchased stock		6 months
Shares purchased and issued under ESPP (in shares)		60,000.00
Weighted average purchase price (in dollars per share) \| $ / shares		$ 43.65
Shares available for purchase under ESPP (in shares)		700,000