CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (12,772)	$ (9,345)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,622	1,871
Depreciation and amortization	249	193
Bad debts expense	192	0
Accretion on marketable securities	(25)	(479)
Amortization of debt issuance costs	65	65
Loss on sale and disposal of property and equipment	0	97
Changes in operating assets and liabilities:
Accounts receivable	2,207	87
Inventory	(256)	(165)
Prepaid expenses and other assets	581	(167)
Accounts payable	76	451
Accrued liabilities and other	(2,294)	314
Net cash used in operating activities	(9,355)	(7,078)
Cash flows from investing activities
Maturities of marketable securities	21,000	17,600
Purchases of marketable securities	(16,777)	(22,741)
Purchases of property and equipment	(884)	(412)
Net cash provided by (used in) investing activities	3,339	(5,553)
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	62,978	0
Proceeds from the exercise of stock options	174	125
Net cash provided by financing activities	63,152	125
Effect of exchange rate changes on cash and cash equivalents	(3)	(53)
Net decrease in cash and cash equivalents	57,133	(12,559)
Cash and cash equivalents at
Beginning of period	10,435	25,120
End of period	67,568	12,561
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	27	66
Purchases of property and equipment included in accounts payable and accrued liabilities	52	140
Public offering costs included in accounts payable	$ 0	$ 167