Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net (loss) income	$ (11,267)	$ (16,887)	$ 8,780
Loss from discontinued operations	0	(12)	(691)
(Loss) income from continuing operations	(11,267)	(16,875)	9,471
Adjustments to reconcile net (loss) income to net cash from operating activities:
Loss on impairment	185	857	0
Depreciation	681	805	266
Stock-based compensation	807	1,360	813
Stock-based compensation reversal	(270)	0	0
Provision for doubtful accounts receivable	(194)	156	39
Provision for slow-moving and obsolete inventories	(1,400)	3,281	1,739
Provision for warranties	(157)	170	255
Amortization of loan origination fees	0	0	40
Loss (gain) on dispositions of property and equipment	203	38	3
Change in operating assets and liabilities:
Accounts receivable	2,240	4,313	(7,493)
Inventories	5,151	(5,018)	(2,602)
Prepaid and other assets	161	(123)	146
Accounts payable	(1,759)	(4,035)	135
Accrued and other liabilities	(260)	(1,389)	1,674
Deferred revenue	5	(93)	(40)
Total adjustments	5,393	322	(5,025)
Net cash (used in) provided by operating activities	(5,874)	(16,553)	4,446
Cash flows from investing activities:
Acquisitions of property and equipment	(162)	(1,624)	(2,242)
Proceeds from the sale of property and equipment	97	27	0
Net cash used in investing activities	(65)	(1,597)	(2,242)
Cash flows from financing activities:
Proceeds from warrants exercised	0	0	2,503
Proceeds from issuances of common stock, net	0	0	23,574
Proceeds from exercise of stock options and purchases through employee stock purchase plan	130	455	346
Common stock withheld in lieu of income tax withholding on vesting of restricted stock units	(49)	0	0
Common stock withheld to satisfy exercise price and income tax withholding on option exercises	0	(309)	0
Payments on other borrowings	0	0	(13)
Net (repayments) proceeds from credit line borrowings	0	0	(453)
Net cash provided by financing activities	81	146	25,957
Effect of exchange rate changes on cash and cash equivalents	(10)	5	0
Net cash (used in) provided by continuing operations	(5,868)	(17,999)	28,161
Cash flows of discontinued operations:
Operating cash flows, net	0	(12)	(691)
Investing cash flows, net	0	0	181
Financing cash flows, net	0	0	(446)
Net cash used in discontinued operations	0	(12)	(956)
Net (decrease) increase in cash and cash equivalents	(5,868)	(18,011)	27,205
Cash and cash equivalents, beginning of year	16,629	34,640	7,435
Cash and cash equivalents, end of year	10,761	16,629	34,640
Classification of cash and cash equivalents:
Cash and cash equivalents, end of year	16,629	34,640	7,435
Supplemental information:
Cash paid in year for interest	2	5	84
Cash paid in year for income taxes	$ 14	$ 51	$ 200