BIAL Agreement - Additional Information (Detail) - B I A L - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Mar. 31, 2017	Sep. 30, 2017
License Agreement [Line Items]
License agreement date		Feb. 09, 2017
Up-front license fees	$ (30)
Milestone payables	$ 115

Up front payments received (paid) under collaborative agreements for sponsored research and development, and licensing fees

No definition available.

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Namespace Prefix:	nbix_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration