CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (25,244)	$ (17,999)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	5,577	3,685
Depreciation and amortization	505	395
Bad debt expense	200	0
Accretion on marketable securities	(20)	(940)
Realized gain on marketable securities	(43)	0
Amortization of debt issuance costs	100	130
Loss on extinguishment of debt	1,534	0
Loss on sale and disposal of property and equipment	80	98
Changes in operating assets and liabilities:
Accounts receivable	1,287	(916)
Inventory	500	(1,092)
Prepaid expenses and other assets	875	102
Accounts payable	(290)	338
Accrued liabilities and other	(2,289)	725
Net cash used in operating activities	(17,228)	(15,474)
Cash flows from investing activities
Maturities of marketable securities	33,500	83,600
Sales of marketable securities	12,592	0
Purchases of marketable securities	(34,768)	(82,516)
Purchases of property and equipment	(1,264)	(893)
Net cash provided by investing activities	10,060	191
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	62,978	0
Proceeds from debt financing	45,297	0
Principal repayments of debt financing	(45,297)	0
Payments of debt issuance costs	(589)	0
Payments of prepayment penalty and lender fees	(843)	0
Proceeds from issuance of common stock under employee stock purchase plan	991	1,263
Proceeds from the exercise of stock options	359	567
Payments of additional initial public offering related costs	0	(167)
Net cash provided by financing activities	62,896	1,663
Effect of exchange rate changes on cash and cash equivalents	6	(4)
Net increase (decrease) in cash and cash equivalents	55,734	(13,624)
Cash and cash equivalents at
Beginning of period	10,435	25,120
End of period	66,169	11,496
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	53	122
Unpaid purchases of property and equipment	145	57
Unpaid debt issuance costs	$ 161	$ 0