XML 55 R35.htm IDEA: XBRL DOCUMENT v3.8.0.1

Summary of Investments Classified as Available-For-Sale Securities (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value		$ 508,578	$ 267,573
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value		0	960
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value		75,362	49,245
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value		414,815	204,436
Domestic and foreign government agencies debt securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value		18,401	12,932
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		261,675	224,236
Gross Unrealized Gains	[1]	1	6
Gross Unrealized Losses	[1]	(459)	(159)
Aggregate Estimated Fair Value		261,217	224,083
Short-term investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			960
Gross Unrealized Gains	[1]		0
Gross Unrealized Losses	[1]		0
Aggregate Estimated Fair Value			$ 960
Short-term investments | Certificates of deposit | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity			1 year
Short-term investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		75,396	$ 49,280
Gross Unrealized Gains	[1]	1	3
Gross Unrealized Losses	[1]	(35)	(38)
Aggregate Estimated Fair Value		$ 75,362	$ 49,245
Short-term investments | Commercial paper | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		1 year	1 year
Short-term investments | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 178,776	$ 168,548
Gross Unrealized Gains	[1]	0	3
Gross Unrealized Losses	[1]	(400)	(117)
Aggregate Estimated Fair Value		$ 178,376	$ 168,434
Short-term investments | Corporate debt securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		1 year	1 year
Short-term investments | Domestic and foreign government agencies debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 7,503	$ 5,448
Gross Unrealized Gains	[1]	0	0
Gross Unrealized Losses	[1]	(24)	(4)
Aggregate Estimated Fair Value		$ 7,479	$ 5,444
Short-term investments | Domestic and foreign government agencies debt securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		1 year	1 year
Long-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 248,753	$ 43,655
Gross Unrealized Gains	[1]	0	0
Gross Unrealized Losses	[1]	(1,392)	(165)
Aggregate Estimated Fair Value		247,361	43,490
Long-term investments | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		237,749	36,149
Gross Unrealized Gains	[1]	0	0
Gross Unrealized Losses	[1]	(1,310)	(147)
Aggregate Estimated Fair Value		$ 236,439	$ 36,002
Long-term investments | Corporate debt securities | Minimum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		1 year	1 year
Long-term investments | Corporate debt securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		2 years	2 years
Long-term investments | Domestic and foreign government agencies debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 11,004	$ 7,506
Gross Unrealized Gains	[1]	0	0
Gross Unrealized Losses	[1]	(82)	(18)
Aggregate Estimated Fair Value		$ 10,922	$ 7,488
Long-term investments | Domestic and foreign government agencies debt securities | Minimum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		1 year	1 year
Long-term investments | Domestic and foreign government agencies debt securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity		2 years	2 years
[1] Unrealized gains and losses are included in other comprehensive loss.

X

- Definition

The term of contractual maturity for available for sale securities, in PnY format.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

+ Details

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

X

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

X

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

X

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

X

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

X

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=nbix_DomesticAndForeignGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=nbix_LongTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: