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Changes to Accrued Cease-Use Liability (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract] |  |
Beginning balance | $ 853 | $ 1,983
Change in estimate | (544) | (830)
Payments | (247) | (300)
Ending balance | $ 62 | $ 853

X
- Definition Amount of liability recorded for the net present value estimated difference between 1) the income to be generated under the Sublease and future subleases, and 2) the Lease obligation over the remaining term of the Lease for the space that is occupied by the subtenant. + References No definition available. + Details
Name: | nbix_CeaseUseLiability
Namespace Prefix: | nbix_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Payments during the period associated with the Cease-use Liability. + References No definition available. + Details
Name: | nbix_CeaseUseLiabilityPayment
Namespace Prefix: | nbix_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The change in the estimated amount of the cease-use liability during the period. + References No definition available. + Details
Name: | nbix_ChangeInEstimateOnCeaseUseLiability
Namespace Prefix: | nbix_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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