| Document and Entity Information | Oct. 29, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 29, 2020 |
| Entity Registrant Name | SEAGEN INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 0-32405 |
| Entity Tax Identification Number | 91-1874389 |
| Entity Address, Address Line One | 21823 30th Drive SE |
| Entity Address, City or Town | Bothell |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98021 |
| City Area Code | 425 |
| Local Phone Number | 527-4000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 |
| Trading Symbol | SGEN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001060736 |
