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