STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (39,334)	$ (15,916)
Adjustments to reconcile net loss:
Depreciation and amortization	375	209
Accretion of investment discount	(88)	(609)
Accretion of debt discount	110	161
Non-cash lease expense	491	433
Stock-based compensation expense	5,652	2,780
Non-cash stock issuance for services rendered	145	116
Other, net	(98)	(141)
Changes in operating assets and liabilities:
Accounts receivable	2,905	(2,801)
Inventories	(4,131)	(894)
Prepaid expenses and other current assets	(2,233)	(4,284)
Accounts payable	639	(745)
Accrued expenses and other liabilities	(4,459)	(2,135)
Net cash used in operating activities	(40,026)	(23,826)
Investing activities
Purchases of property and equipment	(636)	(1,233)
Purchases of investments	(14,907)	(101,037)
Proceeds from sales or maturities of investments	116,703	79,204
Net cash provided by (used in) investing activities	101,160	(23,066)
Financing activities
Payment of debt fees	0	(531)
Proceeds from the exercise of stock options	1,519	769
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	127,232	875
Effect of exchange rate on cash	11	(3)
Increase (decrease) in cash and cash equivalents	188,377	(46,020)
Cash and cash equivalents at beginning of period	22,860	97,288
Cash and cash equivalents at end of period	211,237	51,268
Supplemental cash flow information
Cash paid for interest	$ 947	$ 1,087