Revenue - Collaboration Agreement - Description of good or service to be transferred in contract with customer (Details) - Astellas Collaboration Agreement $ in Millions		3 Months Ended
Jan. 13, 2020 USD ($) item	Mar. 31, 2020 item
Collaboration and License Agreement
Upfront payment received \| $	$ 50.0
Number of co-development targets	3	3
Number of independent targets	2	2

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration