Statement of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (3,026)	$ (7,926)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	813	876
Loss on disposal of property and equipment		20
Stock-based compensation	1,723	1,502
Non-cash gain on warrant revaluation	7
Non-cash interest expense	147	153
Changes in operating assets and liabilities:
Accounts receivable	(1,540)	1,658
Inventory	(505)	133
Prepaid expenses and other current assets	38	200
Accounts payable	(776)	(456)
Accrued liabilities	(1,008)	(907)
Lease liabilities	(73)	(43)
Net cash used in operating activities	(4,200)	(4,790)
Cash flows from investing activities
Purchases of property and equipment	(277)	(461)
Net cash used in investing activities	(277)	(461)
Cash flows from financing activities
Payments on debt		(3,000)
Payments on finance lease obligation	(5)	(5)
Proceeds from exercise of stock options and purchase of shares in employee stock purchase plan	827	150
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs	2,084
Net cash provided by (used in) financing activities	2,906	(2,855)
Net decrease in cash and cash equivalents	(1,571)	(8,106)
Cash and cash equivalents at beginning of period	14,487	23,379
Cash and cash equivalents at end of period	12,916	15,273
Supplementary cash flow information:
Interest paid	197	257
Operating cash flows paid for operating leases	862	837
Financing cash flows paid for finance leases	5	5
Non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating leases		23
Increase of right-of-use asset and lease liability due to lease modification	545
Purchase of property and equipment in accounts payable and accrued liabilities	22	$ 27
Bonus settled in shares of common stock	$ 315