CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities:
Net loss	$ (170,744)	$ (87,442)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	7,951	6,360
Amortization of right-of-use operating lease assets	781	784
Amortization of patents	1,137	999
Amortization of premium on investments, net	8,824	3,842
Amortization of debt issuance costs	2,193	1,527
Stock-based compensation expense	67,882	89,233
Gain on investments	(873)	(9,887)
Loss on early retirement of debt	8,627	0
Non-cash losses related to patents	827	192
Provision for deferred income taxes	0	196
Changes in operating assets and liabilities:
Contracts receivable	52,200	35,200
Inventories	(2,134)	(3,018)
Other current and long-term assets	9,179	1,001
Income taxes payable	551	(4,571)
Accounts payable	(2,819)	(14,939)
Accrued compensation	(35,506)	(14,535)
Accrued liabilities and other current liabilities	(14,914)	2,603
Deferred contract revenue	(50,476)	(59,355)
Net cash used in operating activities	(117,314)	(51,810)
Investing activities:
Purchases of short-term investments	(740,721)	(976,284)
Proceeds from sale of short-term investments	727,859	982,173
Purchases of property, plant and equipment	(6,130)	(18,178)
Acquisition of licenses and other assets, net	(3,182)	(3,023)
Net cash used in investing activities	(22,174)	(15,312)
Financing activities:
Proceeds from equity, net	9,642	16,453
Payments of tax withholdings related to vesting of employee stock awards and exercise of employee stock options	(15,795)	(11,971)
Proceeds from the issuance of 0 percent convertible senior notes	632,500	0
0 percent convertible senior notes issuance costs	(15,551)	0
Repurchase of $247.9 million principal amount of the 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)
Net cash provided by (used in) financing activities	306,965	(86,066)
Effects of exchange rates on cash	(22)	82
Net increase (decrease) in cash and cash equivalents	167,455	(153,106)
Cash and cash equivalents at beginning of period	397,664	683,287
Cash and cash equivalents at end of period	565,119	530,181
Supplemental disclosures of cash flow information:
Interest paid	2,866	3,093
Supplemental disclosures of non-cash investing and financing activities:
Amounts accrued for capital and patent expenditures	$ 278	$ 6,461