CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net loss	$ (72,296)	$ (29,571)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	56	3
Amortization of licenses	60	60
Amortization of premium on investments, net	139	94
Non-cash interest expense for line of credit with Ionis Pharmaceuticals, Inc.	1,507	0
Non-cash sublicensing expense	33,394	0
Stock-based compensation expense	7,122	5,168
Changes in operating assets and liabilities:
Other current and long-term assets	(1,226)	72
Accounts payable	(799)	(137)
Payable to Ionis Pharmaceuticals, Inc.	(13,111)	22,086
Accrued compensation	(1,253)	(390)
Deferred rent	4	44
Accrued liabilities	1,136	(2)
Deferred contract revenue	51,275	0
Net cash provided by (used in) operating activities	6,008	(2,573)
Investing activities:
Purchases of short-term investments	(61,209)	0
Proceeds from the sale of short-term investments	17,820	6,520
Purchases of property, plant and equipment	0	(45)
Net cash (used in) provided by investing activities	(43,389)	6,475
Financing activities:
Proceeds from line of credit from Ionis Pharmaceuticals, Inc.	106,000	0
Offering costs paid	(1,031)	(483)
Net cash provided by (used in) financing activities	104,969	(483)
Net increase (decrease) in cash and cash equivalents	67,588	3,419
Cash and cash equivalents at beginning of period	7,857	29,389
Cash and cash equivalents at end of period	75,445	32,808
Supplemental disclosures of non-cash financing activities:
Unpaid deferred offering costs	$ 473	$ 379