Cash, restricted cash, cash equivalents, and available for sale investments.

No definition available.

Name:	nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments
Namespace Prefix:	nktr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

New accounting pronouncement estimated adjustment to accumulated deficit accrued royalties.

+ References

No definition available.

+ Details

Name:	nktr_NewAccountingPronouncementEstimatedAdjustmentToAccumulatedDeficitAccruedRoyalties
Namespace Prefix:	nktr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

New accounting pronouncement estimated adjustment to accumulated deficit unamortized upfront payment recognized under revenues from contracts with customers.

+ References

No definition available.

+ Details

Name:	nktr_NewAccountingPronouncementEstimatedAdjustmentToAccumulatedDeficitUnamortizedUpfrontPaymentRecognizedUnderRevenuesFromContractsWithCustomers
Namespace Prefix:	nktr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

New accounting pronouncement estimated adjustment to decrease in accumulated deficit.

+ References

No definition available.

+ Details

Name:	nktr_NewAccountingPronouncementEstimatedAdjustmentToDecreaseInAccumulatedDeficit
Namespace Prefix:	nktr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of customers accounted for major accounts receivable.

+ References

No definition available.

+ Details

Name:	nktr_NumberOfCustomersAccountedForMajorAccountsReceivable
Namespace Prefix:	nktr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of reporting units to evaluate goodwill for impairment

+ References

No definition available.

+ Details

Name:	nktr_NumberOfReportingUnitsToEvaluateGoodwillForImpairment
Namespace Prefix:	nktr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Organization and summary of significant accounting policies.

+ References

No definition available.

+ Details

Name:	nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix:	nktr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of accounts receivable customers four.

+ References

No definition available.

+ Details

Name:	nktr_PercentageOfAccountsReceivableCustomersFour
Namespace Prefix:	nktr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of accounts receivable customers one.

+ References

No definition available.

+ Details

Name:	nktr_PercentageOfAccountsReceivableCustomersOne
Namespace Prefix:	nktr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of accounts receivable customers three.

+ References

No definition available.

+ Details

Name:	nktr_PercentageOfAccountsReceivableCustomersThree
Namespace Prefix:	nktr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of accounts receivable customers two.

+ References

No definition available.

+ Details

Name:	nktr_PercentageOfAccountsReceivableCustomersTwo
Namespace Prefix:	nktr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of amount realized upon ultimate settlement.

+ References

No definition available.

+ Details

Name:	nktr_PercentageOfAmountRealizedUponUltimateSettlement
Namespace Prefix:	nktr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

+ Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ 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 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22580-107794

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22583-107794

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22499-107794

+ Details

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleCumulativeEffectOfChangeOnEquityOrNetAssets1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201409Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_NewAccountingPronouncementEarlyAdoptionAxis=us-gaap_NewAccountingPronouncementEarlyAdoptionEffectMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherCurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_RetainedEarningsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_DomesticCountryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxCreditCarryforwardAxis=nktr_StockOptionWindfallDeductionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_StateAndLocalJurisdictionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=nktr_StockOptionsAndRestrictedStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=nktr_ManufacturingLaboratoryAndOtherEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Customer Reporting_Unit shares	Dec. 31, 2016 USD ($) Customer shares	Dec. 31, 2015 shares	Jan. 01, 2017 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities	$ 353,220	$ 389,102
Senior secured notes	$ 250,000
Senior secured notes, maturity date	Oct. 05, 2020
Number of customers accounted for major accounts receivable \| Customer	4	3
Percentage of accounts receivable customers one	43.00%	39.00%
Percentage of accounts receivable customers two	20.00%	32.00%
Percentage of accounts receivable customers three	19.00%	13.00%
Percentage of accounts receivable customers four	14.00%
Number of reporting unit evaluated for goodwill \| Reporting_Unit	1
Minimum percentage of amount realized upon ultimate settlement	50.00%
ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated adjustment to accumulated deficit accrued royalties	$ 11,000
Adoption of New Accounting Principles [Member] \| Other Current Assets [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement				$ 300
Accumulated Deficit [Member] \| Adoption of New Accounting Principles [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement				$ 200
Federal [Member] \| Stock Option Windfall Deductions \| Adoption of New Accounting Principles [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement		$ 20,600
State [Member] \| Stock Option Windfall Deductions \| Adoption of New Accounting Principles [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement		$ 9,800
Stock Options and Restricted Stock Units [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average diluted securities excluded from diluted net loss per share \| shares	20.6	19.9	21.1
Minimum [Member] \| ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated adjustment to decrease in accumulated deficit	$ 11,000
Maximum [Member] \| ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated adjustment to decrease in accumulated deficit	13,000
Estimated adjustment to accumulated deficit unamortized portion of upfront payment amounts recognized	$ 2,000
Buildings [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	20 years
Manufacturing Laboratory and Other Equipment [Member] \| Minimum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	3 years
Manufacturing Laboratory and Other Equipment [Member] \| Maximum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	10 years