Organization and Significant Accounting Policies, Basis of Presentation (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Mar. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Jul. 31, 2017
Subsequent Event [Member]
Basis of Presentation [Abstract]
Sublicense fee to be paid in stock by Akcea for license of AKCEA-AP)(a)-L				$ 75
Additional shares of Akcea stock to be received for license of AKCEA-APO(a)-L (in shares)				2.8
Akcea [Member]
Basis of Presentation [Abstract]
Percentage ownership before IPO	100.00%	100.00%	100.00%
Percentage ownership					75.00%	68.00%	68.00%