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Stockholders' Equity - Additional Information (Detail) (USD $) | 0 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jan. 28, 2014 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Class of Stock [Line Items] |  |  |  |  |
Preferred stock, shares authorized |  | 10,000,000 us-gaap_PreferredStockSharesAuthorized | 10,000,000 us-gaap_PreferredStockSharesAuthorized |  |
Preferred stock, par value |  | $ 0.0001 us-gaap_PreferredStockParOrStatedValuePerShare | $ 0.0001 us-gaap_PreferredStockParOrStatedValuePerShare |  |
Preferred stock, shares designated |  | 0 nktr_PreferredStockShareDesignated | 0 nktr_PreferredStockShareDesignated |  |
Preferred stock, shares issued |  | 0 us-gaap_PreferredStockSharesIssued | 0 us-gaap_PreferredStockSharesIssued |  |
Preferred stock, shares outstanding |  | 0 us-gaap_PreferredStockSharesOutstanding | 0 us-gaap_PreferredStockSharesOutstanding |  |
Proceeds from sale of common stock | $ 117,200,000 us-gaap_ProceedsFromIssuanceOfCommonStock |  |  |  |
Restricted Stock Units outstanding |  | 0 nktr_RestrictedStockUnitsOutstanding |  |  |
Common stock, shares authorized |  | 300,000,000 us-gaap_CommonStockSharesAuthorized | 300,000,000 us-gaap_CommonStockSharesAuthorized |  |
Maximum 401(k) per employee, percentage of annual salary |  | 60.00%nktr_MaximumContributionPerEmployeeAnnualSalaryPercentage |  |  |
Compensation expense in connection with 401(k) retirement plan |  | 900,000 us-gaap_DefinedContributionPlanCostRecognized | 1,000,000 us-gaap_DefinedContributionPlanCostRecognized | 900,000 us-gaap_DefinedContributionPlanCostRecognized |
Severance payment period for executives |  | 12 months |  |  |
Severance payment period for employees |  | 6 months |  |  |
Cash severance payment for chief executive officer |  | 24 months base salary plus annual target incentive pay |  |  |
2012 Performance Incentive Plan [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Additional new shares available for award grants |  | 5,300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized / us-gaap_AwardTypeAxis = nktr_TwoThousandTwelveEquityIncentivePlanMember |  |  |
Share-based compensation plan's share limit reduction for every one restricted stock unit granted |  | 1.5 nktr_ShareBasedCompensationPlansShareLimitForEveryOneShare / us-gaap_AwardTypeAxis = nktr_TwoThousandTwelveEquityIncentivePlanMember |  |  |
Maximum term of stock options under equity incentive plans |  | 8 years |  |  |
2012 Performance Incentive Plan [Member] | Employee [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Service period for stock options granted |  | 4 years |  |  |
2012 Performance Incentive Plan [Member] | Director [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Service period for stock options granted |  | 1 year |  |  |
2000 Non-Officer Equity Incentive Plan [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Maximum term of stock options under equity incentive plans |  | 8 years |  |  |
Restricted Stock Units [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Awards granted |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |
Employee Stock Purchase Plan [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Common stock, shares authorized |  | 2,500,000 us-gaap_CommonStockSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockMember |  |  |
Percentage of purchase price of stock |  | 85.00%nktr_PercentageOfPurchasePriceOfStock / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockMember |  |  |
Maximum [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Matching 401(k) employer contribution, maximum amount |  | 3,000 us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |
Maximum [Member] | 2012 Performance Incentive Plan [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Number of common stock shares available for stock options grants |  | 10,347,140 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_AwardTypeAxis = nktr_TwoThousandTwelveEquityIncentivePlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |
Series A Preferred Stock [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock, shares designated |  | 0 nktr_PreferredStockShareDesignated / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesAPreferredStockMember | 0 nktr_PreferredStockShareDesignated / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesAPreferredStockMember |  | 3,100,000 nktr_PreferredStockShareDesignated / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesAPreferredStockMember
Common Shares [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Common stock, shares issued | 9,775,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 9,775,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |
Legal, accounting fees, filing fees and other offering expenses | 600,000 us-gaap_PaymentsOfStockIssuanceCosts / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |
Underwriting commission and discounts | $ 7,500,000 nktr_UnderwritersCommissionsAndDiscount / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |
Common stock, shares reserved for issuance in equity compensation plans |  | 24,806,565 us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |

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