Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (49,825)	$ (36,364)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,361	854
Stock-based compensation	7,108	2,336
Amortization of right-of-use assets	1,105	739
Accretion of discount on available-for-sale securities	289	(542)
Loss on write down of fixed assets	97	90
Change in fair value of warrant liability		609
Amortization of debt issuance costs	478	322
Changes in operating assets and liabilities:
Accounts receivable	(3,334)	(2,701)
Inventory	(16,338)	(4,096)
Prepaid expenses and other current assets	(1,136)	(1,087)
Other assets	(161)	(1)
Accounts payable	(776)	884
Accrued and other current liabilities	2,841	4,169
Lease liabilities	(494)	(749)
Net cash used in operating activities	(58,785)	(35,537)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of available-for-sale securities	(16,020)	(106,347)
Proceeds from maturities of available-for-sale securities	72,000	32,300
Purchase of property and equipment	(9,846)	(2,287)
Net cash provided by (used in) investing activities	46,134	(76,334)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs paid		100,547
Proceeds from issuance of common stock in private placement		10,000
Payments of offering costs	(179)
Proceed from issuance of common stock from public offering, net of issuance cost paid	83,368
Payments of taxes withheld on net settled vesting of restricted stock units	(862)
Principal payments of term loan	(1,111)
Net proceeds from term loan	3,265
Proceeds from stock option exercises	2,586	1,023
Proceeds from issuance of common stock under employee stock purchase plan	1,795
Proceeds from warrant exercises		110
Net cash provided by financing activities	88,862	111,680
Net increase in cash, cash equivalents and restricted cash	76,211	(191)
Cash, cash equivalents and restricted cash at beginning of period	140,495	40,093
Cash, cash equivalents and restricted cash equivalents at end of period	216,706	39,902
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest paid	403	420
Income tax paid	22	120
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Common stock issued on conversion of convertible preferred stock		152,806
Common stock issued upon net exercise of warrants		133
Common stock warrants issued on conversion of preferred stock warrants and the reclassification of the warrant liability		789
Right-of-use asset obtained in exchange for lease liability	121	73
Property and equipment purchases included in accounts payable and accrued liabilities	233	$ 204
Transfer of fixed assets to inventory	$ 197