CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net loss	$ (87,747)	$ (1,616)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation	7,650	6,138
Amortization of patents	1,356	1,216
Amortization of premium on investments, net	791	5,227
Amortization of debt issuance costs	1,343	1,202
Amortization of convertible senior notes discount	24,781	22,963
Amortization of long-term financing liability for leased facility	0	3,659
Stock-based compensation expense	97,210	63,642
Gain on investment in Regulus Therapeutics, Inc.	0	(374)
Loss on extinguishment of financing liability for leased facility	0	7,689
Non-cash losses related to patents, licensing and property, plant and equipment	482	(403)
Changes in operating assets and liabilities:
Contracts receivable	48,223	65,119
Inventories	1,604	(962)
Other current and long-term assets	(26,573)	(34,866)
Accounts payable	(13,606)	(1,707)
Accrued compensation	(892)	(8,999)
Accrued liabilities and deferred rent	(14,392)	(5,251)
Deferred contract revenue	447,168	31,071
Net cash provided by operating activities	487,398	153,748
Investing activities:
Purchases of short-term investments	(1,156,335)	(589,655)
Proceeds from the sale of short-term investments	568,517	313,860
Purchases of property, plant and equipment	(12,221)	(26,502)
Acquisition of licenses and other assets, net	(3,317)	(4,289)
Proceeds from the sale of Regulus Therapeutics stock	0	2,507
Net cash used in investing activities	(603,356)	(304,079)
Financing activities:
Proceeds from equity awards	18,254	17,672
Proceeds from the issuance of common stock from Akcea Therapeutics, Inc.'s initial public offering, net of underwriters' discount	0	110,438
Proceeds from building mortgage debt, net of issuance costs	0	59,750
Offering costs paid	0	(1,057)
Proceeds from the sale of Akcea Therapeutics, Inc. common stock to Novartis in a private placement	0	50,000
Payment to settle financing liability for leased facility	0	(80,133)
Principal payments on debt and capital lease obligations	0	(3,577)
Net cash provided by financing activities	466,219	224,830
Net increase in cash and cash equivalents	350,261	74,499
Cash and cash equivalents at beginning of period	129,630	84,685
Cash and cash equivalents at end of period	479,891	159,184
Supplemental disclosures of cash flow information:
Interest paid	5,434	4,020
Supplemental disclosures of non-cash investing and financing activities:
Amounts accrued for capital and patent expenditures	2,296	3,475
Purchases of property, plant and equipment included in long-term obligations	3,596	0
Unpaid deferred offering costs	0	638
Novartis [Member]
Financing activities:
Proceeds from issuance of common stock	0	71,737
Biogen [Member]
Financing activities:
Proceeds from issuance of common stock	$ 447,965	$ 0