Fair Value Measurement - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Short-term marketable securities:
Investment in equity securities	$ 17,707
Recurring
Short-term marketable securities:
Total short-term marketable securities	419,264	$ 251,011
Investment in equity securities	17,707
LianBio Warrants	2,878	3,338
Total financial assets	509,493	520,786
Liability
LEO call option liability		5,550
Embedded derivative	1,413	1,340
Total financial liabilities		6,890
Recurring \| Level 1
Short-term marketable securities:
Investment in equity securities	17,707
Total financial assets	87,351	266,437
Recurring \| Level 2
Short-term marketable securities:
Total short-term marketable securities	419,264	251,011
Total financial assets	419,264	251,011
Recurring \| Level 3
Short-term marketable securities:
LianBio Warrants	2,878	3,338
Total financial assets	2,878	3,338
Liability
LEO call option liability		5,550
Embedded derivative	1,413	1,340
Total financial liabilities		6,890
Recurring \| Money Market Funds
Cash equivalents:
Total cash equivalents	69,644	266,437
Recurring \| Money Market Funds \| Level 1
Cash equivalents:
Total cash equivalents	69,644	266,437
Recurring \| U.S. Treasury Bills
Short-term marketable securities:
Total short-term marketable securities		14,999
Recurring \| U.S. Treasury Bills \| Level 2
Short-term marketable securities:
Total short-term marketable securities		14,999
Recurring \| U.S. Treasury Notes
Short-term marketable securities:
Total short-term marketable securities	60,555	45,391
Recurring \| U.S. Treasury Notes \| Level 2
Short-term marketable securities:
Total short-term marketable securities	60,555	45,391
Recurring \| Commercial Paper
Short-term marketable securities:
Total short-term marketable securities	184,277	144,851
Recurring \| Commercial Paper \| Level 2
Short-term marketable securities:
Total short-term marketable securities	184,277	144,851
Recurring \| Corporate Debt Securities
Short-term marketable securities:
Total short-term marketable securities	134,351	45,770
Recurring \| Corporate Debt Securities \| Level 2
Short-term marketable securities:
Total short-term marketable securities	134,351	$ 45,770
Recurring \| Supranational Debt Securities
Short-term marketable securities:
Total short-term marketable securities	40,081
Recurring \| Supranational Debt Securities \| Level 2
Short-term marketable securities:
Total short-term marketable securities	$ 40,081

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