Collaboration, License, and Other Agreements - Alnylam Narratives (Details) - Alnylam Pharmaceuticals, Inc. Collaboration Agreement $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Upfront payment made	$ 400.0
Collaborative arrangement additional payment eligible	$ 200.0
Initial research term	5 years
Potential automatic extension of research term	7 years
Potential optional extension of research term	5 years
Maximum amount of sales milestone payments if total sales achieve specific levels	$ 325.0
Alnylam Pharmaceuticals, Inc. Stock Purchase Agreement
Disaggregation of Revenue [Line Items]
Cash consideration for Stock Purchase Agreement	400.0
Minimum
Disaggregation of Revenue [Line Items]
Extension of research term fee	200.0
Maximum
Disaggregation of Revenue [Line Items]
Extension of research term fee	$ 400.0