Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (9,111)	$ (11,267)	$ (16,887)
Loss from discontinued operations	0	0	(12)
Loss from continuing operations	(9,111)	(11,267)	(16,875)
Adjustments to reconcile net loss to net cash from operating activities:
Loss on impairment	0	185	857
Depreciation	522	681	805
Stock-based compensation	908	807	1,360
Stock-based compensation reversal	0	(270)	0
Provision for doubtful accounts receivable	(9)	(194)	156
Provision for slow-moving and obsolete inventories	17	(1,400)	3,281
Provision for warranties	51	196	170
Amortization of loan origination fees	4	0	0
Loss on dispositions of property and equipment	2	203	38
Change in operating assets and liabilities:
Accounts receivable	1,403	2,240	4,313
Inventories	(2,356)	5,151	(5,018)
Prepaid and other assets	(538)	161	(123)
Accounts payable	2,047	(1,759)	(4,035)
Accrued and other liabilities	240	(613)	(1,389)
Deferred revenue	25	5	(93)
Total adjustments	2,316	5,393	322
Net cash used in operating activities	(6,795)	(5,874)	(16,553)
Cash flows from investing activities:
Acquisitions of property and equipment	(57)	(162)	(1,624)
Proceeds from the sale of property and equipment	246	97	27
Net cash provided by (used in) investing activities	189	(65)	(1,597)
Cash flows from financing activities:
Proceeds from exercise of stock options and purchases through employee stock purchase plan	28	130	455
Common stock withheld in lieu of income tax withholding on vesting of restricted stock units	(62)	(49)	0
Common stock withheld to satisfy exercise price and income tax withholding on option exercises	0	0	(309)
Net proceeds from credit line borrowings	2,219	0	0
Net cash provided by financing activities	2,185	81	146
Effect of exchange rate changes on cash and cash equivalents	(5)	(10)	5
Net cash used in continuing operations	(4,426)	(5,868)	(17,999)
Cash flows of discontinued operations:
Operating cash flows, net	0	0	(12)
Net cash used in discontinued operations	0	0	(12)
Net decrease in cash and cash equivalents	(4,426)	(5,868)	(18,011)
Cash and cash equivalents, beginning of year	10,761	16,629	34,640
Cash and cash equivalents, end of year	6,335	10,761	16,629
Classification of cash and cash equivalents:
Cash and cash equivalents, end of year	10,761	16,629	34,640
Supplemental information:
Cash paid in year for interest	4	2	5
Cash paid in year for income taxes	$ 7	$ 14	$ 51