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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Related Party Transaction [Line Items]
Net losses incurred by the collaboration related to the commercial activities under the TTR License Agreement	$ (5,922)	$ (19,109)	$ (17,724)	$ (34,207)
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	(2,474)	(7,644)	(7,225)	(13,686)
Ionis [Member]
Related Party Transaction [Line Items]
Net loss share from commercial activities under arrangement with Ionis Pharmaceuticals, Inc.	$ (3,448)	$ (11,465)	$ (10,499)	$ (20,521)