Collaboration, License, and Other Agreements - Alnylam Narratives (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Aug. 31, 2019	Apr. 30, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Alnylam Pharmaceuticals, Inc. Stock Purchase Agreement
Disaggregation of Revenue [Line Items]
Cash consideration for Stock Purchase Agreement		$ 400.0
Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront payment made			$ 400.0		$ 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
Minimum | Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Extension of research term fee		$ 200.0
Maximum | Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Extension of research term fee		$ 400.0