Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Cash and Investments in Marketable Securities [Line Items]
Maximum maturity term for debt securities investment	Two years or less
Weighted average maturity term for debt securities investment	One year or less
Available-for-sale securities, sold	$ 11,963,000	$ 8,823,000
Senior secured notes, maturity date	Oct. 05, 2020
Level 1 to level 2 transfers	$ 0	0
Level 2 to level 1 transfers	0	$ 0
Senior secured notes, principal amount	$ 250,000,000
Senior Notes [Member] \| Level 3 [Member]
Cash and Investments in Marketable Securities [Line Items]
Debt instrument redemption terms	We may redeem some or all of these notes at a redemption price equal to 104% of the principal amount of the notes if the redemption date is prior to October 5, 2018, 102% of the principal amount of the notes if the redemption date is prior to October 5, 2019, or 100% of the principal amount of the notes if the redemption date is on or after October 5, 2019, plus, in each case, accrued and unpaid interest to the applicable redemption date.
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member]
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate	7.75%
Senior secured notes, maturity date	Oct. 05, 2020
Minimum cash and investments in marketable securities to be maintained	$ 60,000,000
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member] \| Level 3 [Member]
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate	7.75%
Senior secured notes, maturity date	Oct. 05, 2020
Senior secured notes, principal amount	$ 250,000,000
Senior notes fair value	$ 262,000,000
Senior Notes [Member] \| 7.75% Senior Secured Notes Redemption Date Before October 5, 2018 [Member] \| Level 3 [Member]
Cash and Investments in Marketable Securities [Line Items]
Debt redemption price percentage of principal amount	104.00%
Senior Notes [Member] \| 7.75% Senior Secured Notes Redemption Date Before October 5, 2019 [Member] \| Level 3 [Member]
Cash and Investments in Marketable Securities [Line Items]
Debt redemption price percentage of principal amount	102.00%
Senior Notes [Member] \| 7.75% Senior Secured Notes Redemption Date After October 5, 2019 [Member] \| Level 3 [Member]
Cash and Investments in Marketable Securities [Line Items]
Debt redemption price percentage of principal amount	100.00%

Cash and Investments in Marketable Securities [Line Items]

No definition available.

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

- Definition

Debt investment maturity date description.

+ References

No definition available.

+ Details

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

- Definition

Debt investment maximum maturity period.

+ References

No definition available.

+ Details

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

- Definition

Minimum cash and investments in marketable securities to be maintained.

+ References

No definition available.

+ Details

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

- Definition

Senior notes fair value.

+ References

No definition available.

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

Description of debt redemption features under terms of the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

+ Details

Name:	us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nktr_SevenPointSevenFivePercentSeniorSecuredNotesDueOctoberTwoThousandAndTwentyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nktr_SevenPointSevenFivePercentSeniorSecuredNotesRedemptionDatePriorToOctoberFiveTwoThousandAndEighteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nktr_SevenPointSevenFivePercentSeniorSecuredNotesRedemptionDatePriorToOctoberFiveTwoThousandAndNineteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nktr_SevenPointSevenFivePercentSeniorSecuredNotesRedemptionDateAfterOctoberFiveTwoThousandAndNineteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: