Agreements - CytomX (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Collaborative Agreements disclosures
Revenue from contract with customer		$ 15,025	$ 15,542	$ 28,312	$ 24,126
CytomX | Development milestones
Collaborative Agreements disclosures
Entitled to receive				10,000
Revenue from contract with customer						$ 3,000
CytomX | Phase 2 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer	$ 3,000
CytomX | Regulatory milestones
Collaborative Agreements disclosures
Entitled to receive				50,000
CytomX | Milestone payments
Collaborative Agreements disclosures
Entitled to receive				100,000
Milestone payments plus royalties on the commercial sales | CytomX
Collaborative Agreements disclosures
Entitled to receive				$ 160,000