The percentage decrease in the cost of the rental rates under the terms of the lease

No definition available.

Name:	nbix_BaseRentalReductionPercentage
Namespace Prefix:	nbix_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The year of expiration of the initial lease term.

+ References

No definition available.

+ Details

Name:	nbix_LeaseExpirationYear
Namespace Prefix:	nbix_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Lease extension period.

+ References

No definition available.

+ Details

Name:	nbix_LeaseExtensionPeriod
Namespace Prefix:	nbix_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Letter of credit issued by the bank in lieu of a cash security deposit under the terms of a lease, secured by a deposit of equal amount with that bank.

+ References

No definition available.

+ Details

Name:	nbix_LettersOfCreditCollateral
Namespace Prefix:	nbix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of renewal options under the terms of the lease.

+ References

No definition available.

+ Details

Name:	nbix_NumberOfRenewalOptions
Namespace Prefix:	nbix_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage charged for managing real estate properties.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyManagementFeePercentFee
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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_RealEstatePropertiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The portion of the deferred gain that was recognized in the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=108788860&loc=d3e50609-112754

+ Details

Name:	us-gaap_SaleLeasebackTransactionCurrentPeriodGainRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The portion of the gain that will be recorded as income or a reduction in rent expense in future periods less amounts recognized in the current period.

+ References

+ Details

Name:	us-gaap_SaleLeasebackTransactionDeferredGainNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of an asset, typically cash, provided to a counterparty to provide certain assurance of performance by the entity pursuant to the terms of a written or oral agreement, such as a lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8,17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_SecurityDeposit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of improvements having a life longer than one year that were made for the benefit of one or more tenants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_TenantImprovements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=nbix_AmendedLeaseTermMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=nbix_CommercialLeaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate - Additional Information (Detail) $ in Millions	9 Months Ended		12 Months Ended
Real Estate - Additional Information (Detail) $ in Millions	Sep. 30, 2018 USD ($) RenewalOption	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Apr. 30, 2018 USD ($) ft²	Dec. 31, 2008 USD ($)
Real Estate Properties [Line Items]
Net deferred gain on real estate sale	$ 8.2				$ 39.1
Deferred gain recognized on real estate sale	$ 0.5	$ 1.9
Lease expiration year	2029
Percentage of management fee included in the base annual rent			3.50%
Lease security deposit			$ 4.7
Letter of credit			$ 3.0
Number of times to renew the lease contract \| RenewalOption	2
Lease extension period	10 years
Amended Lease Term
Real Estate Properties [Line Items]
Lease expiration date	Dec. 31, 2029
Percentage reduction in base rental			8.00%
Tenant improvement allowances			$ 13.1
Lease security deposit			$ 3.0
Commercial Lease Agreement
Real Estate Properties [Line Items]
Office space area leased \| ft²				44,718
Lease term				130 months
Commercial Lease Agreement \| Letter of Credit
Real Estate Properties [Line Items]
Lease security deposit				$ 1.0