Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis and Level of the Fair Value Hierarchy (Detail) - Fair value on a recurring basis [Member] - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Investments:
Total assets	$ 810,407	$ 929,845
Liabilities
Contingent milestone payments	40,863	45,258
Total liabilities	40,863	45,258
Investments [Member]
Investments:
Total investments	730,254	677,954
Investments [Member] | US treasury bills [Member]
Investments:
Total investments	478,880	469,386
Investments [Member] | US agency securities [Member]
Investments:
Total investments	251,374	208,568
Cash equivalents [Member] | Money market funds [Member]
Cash equivalents:
Assets, fair value	80,153	251,891
Level 1 [Member]
Investments:
Total assets	80,153	251,891
Level 1 [Member] | Cash equivalents [Member] | Money market funds [Member]
Cash equivalents:
Assets, fair value	80,153	251,891
Level 2 [Member]
Investments:
Total assets	730,254	677,954
Level 2 [Member] | Investments [Member]
Investments:
Total investments	730,254	677,954
Level 2 [Member] | Investments [Member] | US treasury bills [Member]
Investments:
Total investments	478,880	469,386
Level 2 [Member] | Investments [Member] | US agency securities [Member]
Investments:
Total investments	251,374	208,568
Level 3 [Member]
Liabilities
Contingent milestone payments	40,863	45,258
Total liabilities	$ 40,863	$ 45,258