License Agreements and Services Agreement with Ionis, Services Agreement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Services Agreement with Ionis [Abstract]
Payment term after receipt of invoice			30 days
Term of extension for services agreement			6 months
Ionis [Member] | Services Agreement [Member]
Operating expenses:
Services performed by Ionis	$ 1,903	$ 1,075	$ 3,806	$ 2,150
Active pharmaceutical ingredient manufactured by Ionis	7,571		7,571
Out-of-pocket expenses paid by Ionis	1,453	1,275	2,038	2,846
Royalty expenses	613		1,417
Less: commercial share of loss in connection with the TTR license transaction	(3,183)	(11,465)	(10,081)	(20,521)
Less: R&D share of loss (income) in connection with the TTR license transaction	2,243	1,204	3,417	408
Total operating expenses (income) generated by transactions with ions	10,600	(4,911)	8,168	62,883
Sublicensing expenses		3,000		78,000
Plus: distribution to Ionis				13,492
Total net charges generated by transactions with Ionis	10,600	(4,911)	8,168	76,375
(Receivable) payable balance (from) to Ionis at the beginning of the period	(2,432)	(7,206)	(3,231)	18,901
Less: total amounts received from (paid to) Ionis during the period	2,432	4,206	5,663	(28,187)
Less: receivable from Ionis	(5,280)		(5,280)
Less: non-cash sublicensing expenses				(75,000)
Total amount payable (receivable) to (from) Ionis at period end	$ 5,320	$ (7,911)	$ 5,320	$ (7,911)