Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 27, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	0-32405
Entity Registrant Name	SEAGEN INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	91-1874389
Entity Address	21823 30th Drive SE
Entity Address, City or Town	Bothell
Entity Address, State or Province	WA
Postal Zip Code	98021
City Area Code	425
Local Phone Number	527-4000
Title of 12(b) Security	Common Stock, par value $0.001
Trading Symbol	SGEN
Security Exchange Name	NASDAQ
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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		180,306,390
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001060736
Current Fiscal Year End Date	--12-31