Statement of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (6,921)	$ (11,589)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,611	1,297
Loss on disposal of property and equipment		20
Stock-based compensation	2,633	2,397
Non-cash loss on warrant revaluation	2
Non-cash interest expense	231	219
Inventory reserves	1,692
Changes in operating assets and liabilities:
Accounts receivable	(2,368)	1,954
Inventory	(2)	779
Prepaid expenses and other current assets	440	466
Accounts payable	(31)	518
Accrued liabilities	(692)	(1,444)
Lease liabilities	(132)	(72)
Net cash used in operating activities	(3,537)	(5,455)
Cash flows from investing activities
Purchases of property and equipment	(307)	(566)
Net cash used in investing activities	(307)	(566)
Cash flows from financing activities
Payments on debt		(4,840)
Payments of debt issuance costs		(80)
Payments on finance lease obligation	(6)	(8)
Proceeds from exercise of stock options and purchase of shares in employee stock purchase plan	1,206	178
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs	2,084	2,172
Net cash provided by (used in) financing activities	3,284	(2,578)
Net decrease in cash and cash equivalents	(560)	(8,599)
Cash and cash equivalents at beginning of period	14,487	23,379
Cash and cash equivalents at end of period	13,927	14,780
Supplementary cash flow information:
Interest paid	271	373
Operating cash flows paid for operating leases	1,298	1,264
Financing cash flows paid for finance leases	6	8
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	8	33
Bonus settled in shares of common stock	315
Modification of warrant		$ 36
Issuance of warrant	$ 152