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Liability Related to Sale of Future Royalties - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	1 Months Ended		0 Months Ended	12 Months Ended
	Dec. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Feb. 24, 2012	Dec. 31, 2013	Dec. 31, 2012
Liability Related to Sale of Future Royalties [Line Items]
Royalty agreement contingent payment description	As a result of worldwide net sales of MIRCERA for the 12 month periods ended on December 31, 2013 and 2012 not reaching certain minimum thresholds.
Annual interest rate	17.00%nktr_EstimatedAnnualInterestRateOnRoyaltyLiability
Milestone Scenario One [Member]
Liability Related to Sale of Future Royalties [Line Items]
Payment made for milestone not achieved year one		$ 3.0nktr_PaymentMadeForMilestoneNotAchievedYearOne / us-gaap_ContingentConsiderationByTypeAxis = nktr_MilestoneScenarioOneMember
Milestone Scenario Two [Member]
Liability Related to Sale of Future Royalties [Line Items]
Payment made for milestone not achieved year two			7.0nktr_PaymentMadeForMilestoneNotAchievedYearTwo / us-gaap_ContingentConsiderationByTypeAxis = nktr_MilestoneScenarioTwoMember
Purchase and Sale Agreement with RPI [Member]
Liability Related to Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights				124.0nktr_ProceedsFromSaleOfPotentialFutureRoyaltiesGross / us-gaap_TypeOfArrangementAxis = nktr_PurchaseAndSaleAgreementMember
Transaction costs related to sale of potential future royalties				4.4nktr_TransactionCostsRelatedToSaleOfPotentialFutureRoyalties / us-gaap_TypeOfArrangementAxis = nktr_PurchaseAndSaleAgreementMember
CIMZIA and MIRCERA [Member]
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalties from net sales	21.9nktr_RoyaltyRevenueAndNoncashRoyaltyRevenueFromCimziaAndMircera / us-gaap_TypeOfArrangementAxis = nktr_CimziaAndMirceraMember				$ 22.1nktr_RoyaltyRevenueAndNoncashRoyaltyRevenueFromCimziaAndMircera / us-gaap_TypeOfArrangementAxis = nktr_CimziaAndMirceraMember	$ 10.8nktr_RoyaltyRevenueAndNoncashRoyaltyRevenueFromCimziaAndMircera / us-gaap_TypeOfArrangementAxis = nktr_CimziaAndMirceraMember

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Royalty agreement contingent payment description.

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Royalty Revenue And Non-cash Royalty Revenue From Cimzia And Mircera

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Transaction costs related to sale of potential future royalties.

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