CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net loss	$ (41,634)	$ (155,264)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	594	109
Amortization of right-of-use operating lease assets	735
Amortization of intangibles	4,385	815
Amortization of discount/premium on investment securities, net	(470)	197
Non-cash sublicensing expense	75,000
Stock-based compensation expense	29,459	31,239
Changes in operating assets and liabilities:
Accounts receivable	(6,056)	4,777
Other current and long-term assets	(256)	(7,104)
Inventory	(4,369)
Accounts payable	(5,114)	300
Receivable/payable to Ionis Pharmaceuticals, Inc.	(19,548)	9,198
Accrued compensation	799	4,765
Accrued liabilities	(558)	13,237
Income taxes payable	72	(553)
Deferred revenue	(17,948)	(35,882)
Net cash provided by (used in) operating activities	15,091	(134,166)
Investing activities:
Purchases of short-term investments	(111,750)	(105,091)
Proceeds from maturity of short-term investments	155,299	138,580
Purchases of property, plant and equipment	(1,418)	(116)
Net cash provided by investing activities	42,131	33,373
Financing activities:
Proceeds from exercise of common stock options and employee stock purchase plan issuances	9,185	5,141
Distribution to Ionis	(13,492)	(7,792)
Proceeds from issuance of common stock to Ionis in TTR transaction		163,648
Payments of tax withholdings related to exercise of employee stock awards	(10,015)
Net cash (used in) provided by financing activities	(14,322)	160,997
Effect of exchange rates on cash	(25)	19
Net increase in cash and cash equivalents	42,875	60,223
Cash, cash equivalents and restricted cash at beginning of period	88,838	58,367
Cash, cash equivalents and restricted cash at end of period	131,713	118,590
Supplemental disclosures of non-cash operating and financing activities:
Right-of-use assets obtained in exchange for lease liabilities	363
Purchases of property, plant and equipment included in accounts payable and accrued liabilities		1,752
Purchases of property, plant and equipment included in long-term portion of deferred rent liability		3,596
Acquisition of research and development licenses and milestone payments		40,563
Cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets:
Cash and cash equivalents	129,329	116,206
Restricted cash included in deposits and other assets	2,384	2,384
Cash, cash equivalents and restricted cash at end of period	$ 131,713	118,590
Ionis [Member]
Supplemental disclosures of non-cash operating and financing activities:
Purchases of property, plant and equipment included in accounts payable and accrued liabilities		$ 325