Cover - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 17, 2021	Jun. 30, 2020
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	0-24006
Entity Registrant Name	NEKTAR THERAPEUTICS
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3134940
Entity Address, Address Line One	455 Mission Bay Boulevard South
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94158
City Area Code	415
Local Phone Number	482-5300
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	NKTR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 4,100,000,000
Entity Common Stock, Shares Outstanding (in shares)		182,182,063
Documents Incorporated by Reference	Portions of registrant’s definitive Proxy Statement to be filed for its 2020 Annual Meeting of Stockholders are incorporated by reference into Part III hereof. Such Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year covered by this Annual Report on Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0000906709