| Document and Entity Information | Sep. 18, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | SEATTLE GENETICS INC /WA |
| Amendment Flag | false |
| Entity Central Index Key | 0001060736 |
| Document Type | 8-K |
| Document Period End Date | Sep. 18, 2020 |
| Entity Incorporation State 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 |
| Security 12b Title | Common Stock, par value $0.001 |
| Trading Symbol | SGEN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
