Collaboration and License Agreements - Alnylam Narratives (Details) - USD ($)		1 Months Ended	3 Months Ended
	Aug. 31, 2019	Apr. 30, 2019	Jun. 30, 2019
Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront payment made			$ 400,000,000.0
Collaborative arrangement additional payment eligible		$ 200,000,000.0
Initial research term		5 years
Potential extension of research term		5 years
Maximum amount of sales milestone payments if total sales achieve specific levels	$ 325,000,000.0
Alnylam Pharmaceuticals, Inc. Stock Purchase Agreement
Disaggregation of Revenue [Line Items]
Payments made to acquire equity		$ 400,000,000.0
Maximum | Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Initial research term		7 years
Extension of research term fee		$ 400,000,000.0
Minimum | Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Extension of research term fee		$ 200,000,000.0