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Leases - Summary of Minimum Lease Payments for Operating Lease Liabilities (Parenthetical) (Detail) $ in Millions | Sep. 30, 2019 USD ($)
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Leases [Abstract] |
Non-cancelable future minimum lease payments for operating leases that have not yet commenced | $ 47.4

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- Definition Non cancelable future minimum lease payments for operating leases not yet commenced. + References No definition available. + Details
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Namespace Prefix: | nbix_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration