License Agreements and Services Agreement with Ionis, TTR Development, Commercialization, Collaboration and License Agreement (Details)				3 Months Ended		6 Months Ended
	Oct. 17, 2018 USD ($) shares	Aug. 03, 2018 USD ($) shares	Apr. 17, 2018 USD ($) Milestone shares	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) shares	Apr. 16, 2018 shares
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Common stock, shares authorized (in shares) | shares				125,000,000		125,000,000		125,000,000
Intangible assets, net				$ 86,006,000		$ 86,006,000		$ 88,914,000
Amortization expense of milestone payment				1,419,000		2,822,000
Ionis [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Costs incurred by Ionis prior to closing of TTR Agreement			$ 3,100,000
Ionis [Member] | TTR License Agreement [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Upfront licensing fee paid to Ionis						$ 150,000
Shares issued in consideration of upfront licensing fee (in shares) | shares			8,000,000
Number of sales milestones | Milestone			7
Annual worldwide net sales required for subsequent milestone payments to be paid in cash			$ 750,000,000
Notice period for termination of agreement						90 days
Common stock shares issued to Ionis | shares			10,700,000
Stock purchased by Ionis			$ 200,000,000
Common stock, shares authorized (in shares) | shares			125,000,000						100,000,000
Intangible assets, net			$ 600,000
Commercial inotersen inventory acquired from Ionis			$ 4,700,000
Clinical material acquired from Ionis				13,500,000		$ 13,500,000
Percentage of profits and losses from development and commercialization of inotersen paid to Ionis, tier 1			60.00%
Percentage of profits and losses from development and commercialization of inotersen retained, tier 1			40.00%
Percentage of profits and losses from development and commercialization of inotersen paid to Ionis, tier 2			50.00%
Percentage of profits and losses from development and commercialization of inotersen retained, tier 2			50.00%
Percentage of profits and losses from development and commercialization of AKCEA-TTR-L paid to Ionis			50.00%
Percentage of profits and losses from development and commercialization of AKCEA-TTR-L retained			50.00%
Ionis [Member] | TTR License Agreement [Member] | Inotersen [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Maximum amount of payments payable for milestones				110,000,000		110,000,000
Ionis [Member] | TTR License Agreement [Member] | AKCEA-TTR-L [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Maximum amount of payments payable for milestones				145,000,000		145,000,000
Ionis [Member] | TTR License Agreement [Member] | Inotersen and AKCEA-TTR-L [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Maximum amount of payments payable for milestones				1,300,000,000		1,300,000,000
Ionis [Member] | TTR License Agreement [Member] | TEGSEDI [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Common stock shares issued to Ionis | shares	1,671,849	1,597,571
Amount of regulatory approval milestone paid by issuing common stock	$ 50,000,000	$ 40,000,000
Amortization expense of milestone payment				$ 1,400,000	$ 0	$ 2,800,000	$ 0
Ionis [Member] | TTR License Agreement [Member] | TEGSEDI [Member] | Milestone Payment [Member]
TTR Development, Commercialization, Collaboration and License Agreement [Abstract]
Useful life of milestone payment amortized to cost of sales				16 years