Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (56,957)	$ (30,832)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,420	624
Operating lease right-of-use-assets amortization	330
Provision for doubtful accounts	283	255
Stock-based compensation	23,543	14,728
Loss on disposal of property and equipment	123
Changes in operating assets and liabilities:
Accounts receivable	251	(1,058)
Inventories	(2,185)	(3,874)
Prepaid expenses and other assets	(338)	(1,386)
Accounts payable	407	699
Accrued expenses	(184)	2,485
Deferred revenue	417	1
Other liabilities	(283)	(150)
Net cash used in operating activities	(33,173)	(18,508)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of available-for-sale securities	(36,461)
Proceeds from maturities of available-for-sale securities	20,697
Purchases of property and equipment	(268)	(582)
Net cash used in investing activities	(16,032)	(582)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments for restricted stock tax liability on settlement	(225)
Proceeds from issuance of common stock, net of underwriters' discount of $5,338 in 2018	37	78,806
Initial public offering costs		(3,556)
Payments on equipment financing	(338)	(82)
Net cash (used in) provided by financing activities	(526)	75,168
NET CHANGE IN CASH AND CASH EQUIVALENTS	(49,731)	56,078
CASH AND CASH EQUIVALENTS, beginning of year	64,315	8,237
CASH AND CASH EQUIVALENTS, end of year	14,584	64,315
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Settlement of stock-based compensation liability		18,243
Forfeitures of liability-classified awards		1,313
Unpaid property and equipment included in equipment financing		831
Transfer from inventories to property and equipment for lasers	1,505	2,848
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash payments for interest	49	11
Cash payments for taxes	$ 30	$ 5