STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (16,245)	$ (8,266)
Adjustments to reconcile net loss:
Depreciation and amortization	187	103
Accretion of investment discount	(80)	(309)
Accretion of debt discount	54	110
Non-cash lease expense	243	204
Stock-based compensation expense	2,749	1,391
Non-cash stock issuance for services rendered	72	58
Other, net	(89)	(141)
Changes in operating assets and liabilities:
Accounts receivable	2,092	(385)
Inventories	(1,411)	(439)
Prepaid expenses and other current assets	775	212
Accounts payable	1,372	(222)
Accrued expenses and other liabilities	(4,494)	(3,258)
Net cash used in operating activities	(14,775)	(10,942)
Investing activities
Purchases of property and equipment	(255)	(275)
Purchases of investments	(14,907)	(40,573)
Proceeds from sales or maturities of investments	82,403	56,804
Net cash provided by investing activities	67,241	15,956
Financing activities
Payment of debt fees	0	(531)
Proceeds from the exercise of stock options	787	165
Net cash provided by (used in) financing activities	787	(366)
Effect of exchange rate on cash	4	9
Increase in cash and cash equivalents	53,257	4,657
Cash and cash equivalents at beginning of period	22,860	97,288
Cash and cash equivalents at end of period	76,117	101,945
Supplemental cash flow information
Cash paid for interest	$ 471	$ 771