Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (13,301)	$ (11,227)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	95	135
Noncash interest expense	281	244
Amortization of intangible assets	152	152
Inventory excess and obsolescence charge	767	916
Change in fair value of warrants		38
Stock‑based compensation expense	943	119
Change in operating assets and liabilities:
Accounts receivable	238	(599)
Inventory	(750)	(1,169)
Prepaid expenses and other assets	823	(156)
Accounts payable	(2,096)	(1,312)
Accrued expenses and other liabilities	(859)	(123)
Foreign currency remeasurement loss	45
Net cash used in operating activities	(13,662)	(12,982)
Cash flows from investing activities:
Proceeds from the sale and maturity of short-term investments	9,289
Payment for intangible asset		(500)
Purchase of property and equipment	(96)	(89)
Net cash provided by (used in) investing activities	9,193	(589)
Cash flows from financing activities:
Proceeds from underwritten public offering, net of underwriting discounts, commissions and offering costs	45,120
Payment of initial public offering costs	(522)
Proceeds from issuance of Series B redeemable convertible preferred stock, net of offering costs		12,158
Proceeds from exercise of stock options	44	8
Net cash provided by financing activities	44,642	12,166
Effect of exchange rate on cash	(4)
Net increase (decrease) in cash and cash equivalents	40,169	(1,405)
Cash and cash equivalents, beginning of period	45,302	17,278
Cash and cash equivalents, end of period	85,471	15,873
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	1,482	1,582
Supplemental disclosures of noncash investing and financing activities:
Accretion of redeemable convertible preferred stock		4,787
Offering costs in accounts payable and accrued expense and other current liabilities	398	32
Intangible assets in accrued expenses and other liabilities		2,000
Issuance of common stock for early exercised stock options	$ 2	$ 3