CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net loss	$ (4,266)	$ (4,362)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	4,271	3,422
Stock-based compensation expense	4,263	957
Change in fair value of convertible preferred stock warrant liability		1,383
Loss (gain) on disposal of fixed assets and lease impairment	(70)
Amortization of debt discount		286
Non-cash interest expense related to debt costs		139
Changes in operating assets and liabilities:
Accounts receivable	(769)	(894)
Inventories	3,464	(8,656)
Prepaid expenses and other assets	2,862	(2,367)
Accounts payable	(1,096)	356
Accrued and other liabilities	2,914	2,328
Net cash provided by (used in) operating activities	11,573	(7,408)
Cash flows from investing activities
Purchases of property and equipment	(4,434)	(2,952)
Proceeds from sales of Property and equipment	70
Proceeds from sales and maturities of short-term investments	32,488
Purchases of short-term investments	(42,657)	(1,850)
Net cash used in investing activities	(14,533)	(4,802)
Cash flows from financing activities
Repayments on short and long-term borrowings		(7,846)
Repayments on line of credit		(5,000)
Proceeds from line of credit		10,000
Proceeds from exercise of stock options, purchase rights, and preferred stock warrants	4,064	944
Purchases of IP licenses	(26)	(195)
Payment of costs related to initial public offering	(276)	(1,057)
Net cash provided by (used in) financing activities	3,762	(3,154)
Net increase (decrease) in cash and cash equivalents	802	(15,364)
Cash and cash equivalents at beginning of period	8,040	28,893
Cash and cash equivalents at end of period	8,842	13,529
Supplemental disclosures of cash flow information
Cash paid for interest	17	707
Cash paid for income taxes	193	41
Non-cash financing and investing transactions
Transfer of fair value of warrants to equity from liabilities upon warrant exercise		10,738
Cashless exercises of warrants, net of assumed proceeds from shares	1,175
Unpaid costs related to initial public offering		608
Property and equipment received and accrued	$ 100	$ 503