CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue:
Revenue	$ 22,377	$ 26,623	$ 38,451	$ 190,439
Expenses:
Cost of sales - intangible asset amortization	1,418	1,419	2,837	2,822
Research and development	29,731	20,271	47,086	119,890
Selling, general and administrative	42,139	50,740	88,385	95,342
Total expenses	73,468	65,329	134,801	202,938
Loss from operations	(51,091)	(38,706)	(96,350)	(12,499)
Other income (expense):
Investment income	1,055	1,571	2,826	2,795
Other expense	(146)	(28)	(276)	(140)
Loss before income tax expense	(50,182)	(37,163)	(93,800)	(9,844)
Income tax benefit (expense)	605	(160)	1,373	(292)
Net loss	(49,577)	(37,323)	(92,427)	(10,136)
Ionis [Member]
Expenses:
Net loss share from commercial activities under arrangement with Ionis Pharmaceuticals, Inc.	(3,448)	(11,465)	(10,499)	(20,521)
Common Stock [Member] | Ionis [Member]
Other income (expense):
Net loss	$ (37,665)	$ (28,244)	$ (70,348)	$ (4,380)
Net loss per share, basic and diluted (in dollars per share)	$ (0.49)	$ (0.40)	$ (0.91)	$ (0.06)
Weighted-average shares outstanding, basic and diluted (in shares)	77,094,682	70,221,338	77,094,682	69,406,181
Common Stock [Member] | Others [Member]
Other income (expense):
Net loss per share, basic and diluted (in dollars per share)	$ (0.49)	$ (0.40)	$ (0.91)	$ (0.26)
Weighted-average shares outstanding, basic and diluted (in shares)	24,381,592	22,573,900	24,195,990	22,351,368
Product [Member]
Revenue:
Revenue	$ 16,364	$ 9,865	$ 31,523	$ 16,619
Expenses:
Cost of product/license	3,628	1,364	6,992	2,405
Licensing [Member]
Revenue:
Revenue		6,036		6,036
Expenses:
Cost of product/license		3,000		3,000
Research and Development and License Revenue Under Collaborative Agreement [Member]
Revenue:
Revenue	$ 6,013	$ 10,722	$ 6,928	$ 167,784