License Agreements and Services Agreement with Ionis, Services Agreement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 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
Sublicensing expenses		75,000
Out-of-pocket expenses paid by Ionis	585	1,571
Royalty expenses	804
Less: commercial share of loss in connection with the TTR license transaction	(6,898)	(9,056)
Less: R&D share of loss (income) in connection with the TTR license transaction	1,174	(796)
Total operating (income) expenses generated by transactions with ions	(2,432)	67,794
Plus: distribution to Ionis		13,492
Total net charges generated by transactions with Ionis	(2,432)	81,286
(Receivable) payable balance (from) to Ionis at the beginning of the period	(3,231)	18,901
Less: total amounts received from (paid to) Ionis during the period	3,231	(32,393)
Less: non-cash sublicensing expenses		(75,000)
Total amount (receivable) payable (from) to Ionis at period end	$ (2,432)	$ (7,206)