Summary of Significant Accounting Policies - Revenue Recognition (Details)	6 Months Ended
	Jun. 30, 2020 item
Oxford BioTherapeutics Ltd Member
Summary of Significant Accounting Policies
Number of single-target licenses	1
Bayer
Summary of Significant Accounting Policies
Number of single-target licenses	1
Biotest
Summary of Significant Accounting Policies
Number of single-target licenses	1
CytomX
Summary of Significant Accounting Policies
Number of single-target licenses	2
Fusion Pharmaceuticals
Summary of Significant Accounting Policies
Number of single-compound licenses	1
Novartis
Summary of Significant Accounting Policies
Number of single-target licenses	5
Roche
Summary of Significant Accounting Policies
Number of single-target licenses	5
Sanofi
Summary of Significant Accounting Policies
Number of single-target licenses	5
Takeda
Summary of Significant Accounting Policies
Number of single-target licenses	1
Debiopharm
Summary of Significant Accounting Policies
Number of single-compound licenses	1