STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (49,719)	$ (24,163)
Adjustments to reconcile net loss:
Depreciation and amortization	587	342
Accretion of investment discount	(66)	(846)
Accretion of debt discount	166	214
Non-cash lease expense	743	665
Stock-based compensation expense	8,963	4,304
Non-cash stock issuance for services rendered	217	174
Other, net	(89)	(143)
Changes in operating assets and liabilities:
Accounts receivable	(7,921)	(4,378)
Inventories	(3,132)	(2,008)
Prepaid expenses and other current assets	(15)	(1,908)
Accounts payable	2,262	1,444
Accrued expenses and other liabilities	(931)	(467)
Net cash used in operating activities	(48,935)	(26,770)
Investing activities
Purchases of property and equipment	(1,851)	(2,297)
Purchases of investments	(52,721)	(143,524)
Proceeds from sales or maturities of investments	129,803	122,254
Net cash provided by (used in) investing activities	75,231	(23,567)
Financing activities
Payment of debt fees	0	(531)
Proceeds from the exercise of stock options	3,831	961
Proceeds from the sale of common stock	124,654	0
Proceeds from issuance of common stock from employee stock purchase plan	1,059	637
Net cash provided by financing activities	129,544	1,067
Effect of exchange rate on cash	5	26
Increase (decrease) in cash and cash equivalents	155,845	(49,244)
Cash and cash equivalents at beginning of period	22,860	97,288
Cash and cash equivalents at end of period	178,705	48,044
Supplemental cash flow information
Cash paid for interest	$ 1,422	$ 1,562