Fair value - Schedule of Fair Value Hierarchy of Assets Carried at Fair Value and Measured on a Recurring Basis (Details) - Fair Value Measurements Recurring - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 809,522	$ 1,418,984
US Treasury Securities \| Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	808,418	1,415,130
Equity Securities \| Other Non-current Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,104	3,854
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	809,522	1,418,984
Quoted prices in active markets for identical assets (Level 1) \| US Treasury Securities \| Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	808,418	1,415,130
Quoted prices in active markets for identical assets (Level 1) \| Equity Securities \| Other Non-current Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,104	3,854
Other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Other observable inputs (Level 2) \| US Treasury Securities \| Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Other observable inputs (Level 2) \| Equity Securities \| Other Non-current Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Significant unobservable inputs (Level 3) \| US Treasury Securities \| Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Significant unobservable inputs (Level 3) \| Equity Securities \| Other Non-current Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 0	$ 0

Seagen Inc. 10-Q