Summary of Significant Accounting Policies - Contract Balances from Contracts with Customers - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Revenue recognized in the period from:
Revenue from contract with customer	$ 13,287,000	$ 8,584,000
Deferred revenue	127,510,000	146,010,000	$ 127,432,000	$ 80,802,000
Contract asset	990,000		3,631,000	$ 500,000
Contract liability	123,000		309,000
Contract Liabilities, Impact Of Netting	361,000
Revenue previously deferred	283,000	79,000
Milestone earned, included in accounts receivable	3,000,000	500,000
Probable milestone earned and paid		0
Milestone related
Revenue recognized in the period from:
Revenue from contract with customer	500,000
License and milestone fees
Revenue recognized in the period from:
Revenue from contract with customer	283,000	79,000
CytomX | License and milestone fees
Revenue recognized in the period from:
Revenue from contract with customer	200,000
CytomX | Probable Milestone
Revenue recognized in the period from:
Contract asset			2,700,000
Contract liability			$ 300,000
Kadcyla | Royalty revenue
Revenue recognized in the period from:
Deferred revenue	65,200,000
Other Collaborators | Technological Improvements
Revenue recognized in the period from:
Amortization of deferred revenue	$ 83,000	$ 79,000