License Agreements and Services Agreement with Ionis - Summary of Loss Share Related to Commercial Activities Under TTR Agreement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Related Party Transaction [Line Items]
Net losses incurred by the collaboration related to the commercial activities under the TTR License Agreement	$ (11,802)	$ (15,098)
Akcea [Member]
Related Party Transaction [Line Items]
Akcea's share of commercial losses under the TTR License Agreement reflected in our condensed consolidated statement of operations	(4,751)	(6,042)
Ionis [Member]
Related Party Transaction [Line Items]
Net loss share from commercial activities under arrangement with Ionis Pharmaceuticals, Inc.	$ (7,051)	$ (9,056)