License Agreements and Services Agreement with Ionis, Services Agreement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Expenses Generated by Transactions with Ionis [Abstract]
Payable balance to Ionis at the beginning of the period			$ 14,365
Total amount payable to Ionis at period end	$ 27,137		$ 27,137
Ionis [Member] | Services Agreement [Member]
Services Agreement with Ionis [Abstract]
Payment term after receipt of invoice			30 days
Term of extension for services agreement			6 months
Operating Expenses Generated by Transactions with Ionis [Abstract]
Services performed by Ionis	6,045	$ 2,998	$ 7,990	$ 5,955
Active pharmaceutical ingredient manufactured by Ionis	0	2,930	5,229	6,013
Commercial inventory manufactured by Ionis	5,996	0	5,996	0
Sublicensing expenses	0	0	0	48,394
Out-of-pocket expenses paid by Ionis	16,029	5,316	23,016	17,189
Total expenses generated by transactions with Ionis	28,070	11,244	42,231	77,551
Payable balance to Ionis at the beginning of the period	27,737	15,000	14,365	24,355
Less: total amounts paid to Ionis during the period	(27,737)	(15,000)	(28,526)	(57,268)
Less: receivable from Ionis	(933)	0	(933)	0
Less: non-cash sublicensing expenses	0	0	0	(33,394)
Total amount payable to Ionis at period end	$ 27,137	$ 11,244	$ 27,137	$ 11,244