CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Revenue	$ 18,321	$ 5,713	$ 35,429	$ 11,807
Expenses:
Research and development	39,457	18,487	67,427	83,282
General and administrative	42,287	6,915	61,752	11,590
Total operating expenses	81,744	25,402	129,179	94,872
Loss from operations	(63,423)	(19,689)	(93,750)	(83,065)
Other income (expense):
Investment income	1,546	245	2,414	308
Interest expense	0	(965)	0	(1,507)
Other income (expense)	45	50	(123)	50
Loss before income tax expense	(61,832)	(20,359)	(91,459)	(84,214)
Income tax expense	(214)	0	(214)	0
Net loss	(62,046)	(20,359)	(91,673)	(84,214)
Preferred Stock [Member]
Other income (expense):
Net loss	$ 0	$ (20,359)	$ 0	$ (84,214)
Net loss per share, basic and diluted (in dollars per share)	$ 0	$ (0.70)	$ 0	$ (2.92)
Weighted-average shares outstanding, basic and diluted (in shares)	0	28,884,540	0	28,884,540
Common Stock [Member] | Ionis [Member]
Other income (expense):
Net loss	$ (43,814)	$ 0	$ (63,198)	$ 0
Net loss per share, basic and diluted (in dollars per share)	$ (0.72)	$ 0	$ (1.19)	$ 0
Weighted-average shares outstanding, basic and diluted (in shares)	60,832,494	0	53,182,685	0
Common Stock [Member] | Others [Member]
Other income (expense):
Net loss per share, basic and diluted (in dollars per share)	$ (0.85)	$ 0	$ (1.33)	$ 0
Weighted-average shares outstanding, basic and diluted (in shares)	21,492,157	0	21,332,650	0
Research and Development Under Collaborative Agreement [Member]
Revenue:
Revenue	$ 18,321	$ 5,713	$ 35,429	$ 11,807