Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (44,124)	$ (22,011)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	530	325
Stock-based compensation expense	2,023	685
Change in fair value of redeemable convertible preferred stock warrant liability	21,030	4,907
Amortization of debt discount and debt issuance costs	34	57
Amortization of right-of-use asset	440
Non-cash interest expense	595	1,153
Provision for sales returns and allowances	1,163	1,255
Provision for excess and obsolete inventories	78	0
Changes in assets and liabilities
Accounts receivable	(3,575)	(1,515)
Inventories	(3,609)	(1,925)
Prepaid expenses and other current assets	(2,096)	(437)
Other assets	764	(58)
Accounts payable	712	(565)
Accrued liabilities	2,255	1,379
Other liabilities	(569)	445
Net cash used in operating activities	(24,349)	(16,305)
Cash flows from investing activities
Purchases of property and equipment	(337)	(2,168)
Net cash used in investing activities	(337)	(2,168)
Cash flows from financing activities
Proceeds from long-term debt	0	15,000
Proceeds from initial public offering, net of underwriting discount, commissions and offering costs paid	109,352	0
Proceeds from issuance of common stock	806	649
Non-controlling interest	0	1
Net cash provided by financing activities	111,973	15,650
Net change in cash, cash equivalents and restricted cash	87,287	(2,823)
Cash, cash equivalents and restricted cash, beginning of period	25,300	33,841
Cash, cash equivalents and restricted cash, end of period	112,587	31,018
Supplemental disclosure of cash flow information
Cash paid for interest	3,107	1,855
Non-cash investing and financing activities:
Accounts payable and accrued liabilities for purchases of property and equipment	9	26
Landlord paid tenant improvements	0	794
Right-of-use asset obtained in exchange for lease obligation	3,982
Net exercise of convertible preferred stock warrants to preferred stock	37,121	0
Conversion of convertible preferred stock to common stock upon initial public offering	144,140	0
Redeemable Convertible Preferred Stock
Cash flows from financing activities
Proceeds from exercise of warrants	1,784	0
Common Stock Warrant
Cash flows from financing activities
Proceeds from exercise of warrants	$ 31	$ 0