Agreements - CytomX (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Feb. 29, 2016	Jan. 31, 2014	Mar. 31, 2018	Mar. 31, 2017
Collaborative Agreements disclosures
License and milestone fees			$ 11,540	$ 18,730
CytomX
Collaborative Agreements disclosures
Payments received under collaboration agreement	$ 13,000	$ 0
License and milestone fees	12,700
Potential milestone payments	160,000
CytomX | Development milestones
Collaborative Agreements disclosures
Potential milestone payments	10,000
CytomX | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payments	3,000
CytomX | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payments	50,000
CytomX | Sales milestones
Collaborative Agreements disclosures
Potential milestone payments	$ 100,000