CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net loss	$ (2,201)	$ (3,357)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	2,755	2,206
Stock-based compensation expense	2,140	549
Change in fair value of convertible preferred stock warrant liability		1,700
Loss (Gain) on disposal of fixed assets and lease impairment	(70)
Amortization of debt discount		205
Non-cash interest expense related to debt costs		113
Changes in operating assets and liabilities:
Accounts receivable	(988)	(2,546)
Inventories	2,071	(2,229)
Prepaid expenses and other assets	2,570	(2,997)
Accounts payable	(2,527)	(2,690)
Accrued and other liabilities	633	291
Net cash provided by (used in) operating activities	4,383	(8,755)
Cash flows from investing activities
Purchases of property and equipment	(1,981)	(1,873)
Proceeds from sales of PP&E	70
Proceeds from sales and maturity of short-term investments	20,553
Purchases of short-term investments	(21,137)	(902)
Net cash used in investing activities	(2,495)	(2,775)
Cash flows from financing activities
Repayments on short and long-term borrowings		(5,054)
Proceeds from line of credit		5,000
Proceeds from exercise of stock options, purchase rights, and preferred stock warrants	3,248	817
Purchases of IP licenses	(26)	(130)
Payment of costs related to initial public offering	(276)	(627)
Net cash provided by financing activities	2,946	6
Net increase (decrease) in cash and cash equivalents	4,834	(11,524)
Cash and cash equivalents at beginning of period	8,040	28,893
Cash and cash equivalents at end of period	12,874	17,369
Supplemental disclosures of cash flow information
Cash paid for interest		707
Cash paid for income taxes	80	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	550
Unpaid costs related to initial public offering		269
Property and equipment received and accrued	$ 1,002	$ 184