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v3.20.1

Fair Value Measurements - Additional Information (Detail) - Discount for Lack of Marketability | Mar. 31, 2020
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Minimum |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |
Valuation analysis of equity securities | 18.50%
Maximum |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |
Valuation analysis of equity securities | 30.00%
Weighted Average |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |
Valuation analysis of equity securities | 26.20%

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- Definition Equity securities measurement input. + References No definition available. + Details
Name: | nbix_EquitySecuritiesMeasurementInput
Namespace Prefix: | nbix_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |