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	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Related Party Transaction [Line Items]
Net losses incurred by the collaboration related to the commercial activities under the TTR Agreement	$ (14,814)	$ (49,021)
Akcea [Member]
Related Party Transaction [Line Items]
Akcea's share of commercial losses under the TTR Agreement reflected in our condensed consolidated statements of operations	(5,925)	(19,611)
Ionis [Member]
Related Party Transaction [Line Items]
Net loss share from commercial activities under arrangement with Ionis Pharmaceuticals, Inc.	$ (8,889)	$ (29,410)