STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net loss	$ (16,216)	$ (16,245)
Adjustments to reconcile net loss:
Depreciation and amortization	234	187
Amortization (accretion) of investment premium (discount)	30
Amortization (accretion) of investment premium (discount)		(80)
Accretion of debt discount	58	54
Non-cash lease expense	171	243
Stock-based compensation expense	5,997	2,749
Non-cash stock issuance for services rendered	73	72
Other, net	(8)	(89)
Changes in operating assets and liabilities:
Accounts receivable	3,381	2,092
Inventories	(2,905)	(1,411)
Prepaid expenses and other current assets	356	775
Accounts payable	1,477	1,372
Accrued expenses and other liabilities	(3,049)	(4,494)
Net cash used in operating activities	(10,401)	(14,775)
Investing activities
Purchases of property and equipment	(1,321)	(255)
Purchases of investments	0	(14,907)
Proceeds from sales or maturities of investments	0	82,403
Net cash (used in) provided by investing activities	(1,321)	67,241
Financing activities
Proceeds from the exercise of stock options	3,550	787
Net cash provided by financing activities	3,550	787
Effect of exchange rate on cash	2	4
(Decrease) increase in cash and cash equivalents	(8,170)	53,257
Cash and cash equivalents at beginning of period	190,518	22,860
Cash and cash equivalents at end of period	182,348	76,117
Supplemental cash flow information
Cash paid for interest	466	471
Purchases of property and equipment in accounts payable	$ 1,209	$ 0