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Employment Benefits (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Employment Benefits [Abstract] |  |  |
Employee contribution limit per calendar year for employees under 50 years of age | $ 19,000 |  |
Employee contribution limit per calendar year for employees over 50 years of age | 25,000 |  |
Matching contributions | $ 6,400,000 | $ 5,700,000 | $ 3,000,000.0

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- Definition The limit of annual employee contributions to the plan per calendar year by eligible employees who are over 50 years of age. + References No definition available. + Details
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Namespace Prefix: | ions_
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Period Type: | duration

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- Definition The limit of annual employee contributions to the plan per calendar year by eligible employees who are under 50 years of age. + References No definition available. + Details
Name: | ions_DefinedContributionPlanEmployeeContributionLimitByPlanParticipantsUnderFiftyYearsAge
Namespace Prefix: | ions_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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