CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities:
Net loss	$ (253,210)	$ (124,056)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	11,665	9,713
Amortization of right-of-use operating lease assets	1,171	1,356
Amortization of patents	1,740	1,526
Amortization of premium on investments, net	13,515	7,812
Amortization of debt issuance costs	3,586	2,388
Stock-based compensation expense	98,419	135,077
Gain on investments	(933)	(10,722)
Loss on early retirement of debt	8,627	0
Non-cash losses related to patents	1,150	616
Provision for deferred income taxes	0	1,649
Changes in operating assets and liabilities:
Contracts receivable	67,136	24,057
Inventories	(965)	(1,468)
Other current and long-term assets	10,358	(5,647)
Income taxes (payable) receivable	134	(23,674)
Accounts payable	(10,737)	(10,970)
Accrued compensation	(33,408)	(8,967)
Accrued liabilities and other current liabilities	(19,526)	13,195
Deferred contract revenue	(71,610)	(73,970)
Net cash used in operating activities	(172,888)	(62,085)
Investing activities:
Purchases of short-term investments	(930,963)	(1,376,631)
Proceeds from sale of short-term investments	1,051,857	1,497,433
Purchases of property, plant and equipment	(9,453)	(29,971)
Acquisition of patents, net	(4,459)	(4,203)
Purchase of Bicycle Therapeutics plc common stock	(7,185)	0
Net cash provided by investing activities	99,797	86,628
Financing activities:
Proceeds from equity, net	11,564	29,450
Payments of tax withholdings related to vesting of employee stock awards and exercise of employee stock options	(16,285)	(12,960)
Proceeds from issuance of 0 percent convertible senior notes	632,500	0
0 percent convertible senior notes issuance costs	(15,525)	0
Repurchase of $247.9 million principal amount of 1 percent convertible senior notes	(256,963)	0
Proceeds from issuance of warrants	89,752	0
Purchase of note hedges	(136,620)	0
Repurchases and retirements of common stock	0	(90,548)
Payments of transaction costs for Akcea merger	0	(1,071)
Net cash provided by (used in) financing activities	308,423	(75,129)
Effects of exchange rates on cash	(43)	358
Net increase (decrease) in cash and cash equivalents	235,289	(50,228)
Cash and cash equivalents at beginning of period	397,664	683,287
Cash and cash equivalents at end of period	632,953	633,059
Supplemental disclosures of cash flow information:
Interest paid	3,527	3,700
Income taxes paid	3	23,532
Supplemental disclosures of non-cash investing and financing activities:
Amounts accrued for capital and patent expenditures	1,811	6,576
Amounts accrued for Akcea merger transaction costs	$ 0	$ 8,103