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

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.

No definition available.

Name:	nbix_CeaseUseLiability
Namespace Prefix:	nbix_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant