Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic and Diluted Net Loss Per Share [Abstract]
Net loss	$ (62,046)	$ (20,359)	$ (91,673)	$ (84,214)
Distribution to Ionis	(7,792)	0	(7,792)	0
Distributable losses	(69,838)	(20,359)	(99,465)	(84,214)
Preferred Stock [Member]
Basic and Diluted Net Loss Per Share [Abstract]
Net loss	$ 0	$ (20,359)	$ 0	$ (84,214)
Weighted-average shares outstanding owned	0	28,884,540	0	28,884,540
Basic loss per common share owned	$ 0	$ (0.70)	$ 0	$ (2.92)
Common Stock [Member]
Basic and Diluted Net Loss Per Share [Abstract]
Weighted-average shares outstanding owned	82,324,651		74,515,335
Common Stock [Member] | Ionis [Member]
Basic and Diluted Net Loss Per Share [Abstract]
Net loss	$ (43,814)	$ 0	$ (63,198)	$ 0
Distributable losses	$ (51,606)	$ 0	$ (70,990)	$ 0
Weighted-average shares outstanding owned	60,832,494	0	53,182,685	0
Basic loss per common share owned	$ (0.72)	$ 0	$ (1.19)	$ 0
Common Stock [Member] | Others [Member]
Basic and Diluted Net Loss Per Share [Abstract]
Distributable losses	$ (18,232)	$ 0	$ (28,475)	$ 0
Weighted-average shares outstanding owned	21,492,157	0	21,332,650	0
Basic loss per common share owned	$ (0.85)	$ 0	$ (1.33)	$ 0