Basis of Presentation and Significant Accounting Policies - Contract Balances from Contracts with Customers - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Feb. 28, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue	$ 59,247	$ 109,272	$ 59,247	$ 109,272		$ 92,068	$ 110,109
Revenue from contract with customer	14,162	16,948	52,240	32,654
Revenue recognized, previously deferred	10,864	765	36,624	837
License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer	6,973	$ 252	37,865	409
Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue						28,500
License agreement upfront payment receivable						$ 45,000
Lilly
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
License agreement upfront payment receivable					$ 13,000
Lilly | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer			9,200
Lilly | Upfront payment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue	$ 13,000		13,000
KADCYLA
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net proceeds from sale of residual rights to receive royalty payments				500
KADCYLA | Royalty revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net proceeds from sale of residual rights to receive royalty payments			8,000
Viridian | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer			$ 200
Revenue recognized, previously deferred				200
CytomX and Novartis | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognized, previously deferred				$ 100