Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net loss	$ (7,431)	$ (8,701)
Adjustments to reconcile net loss to net cash used in operating activities:
Mark-down of inventory		641
Depreciation and amortization	1,129	1,078
Stock-based compensation	535	924
Impairment of long-lived assets	1,676
Gain on disposal of long-lived assets	(11)
Changes in operating assets and liabilities:
Trade accounts receivable	(183)	37
Inventory	19	(281)
Prepaid expenses and other current assets	41	(37)
Accounts payable and accrued liabilities	384	64
Deferred revenue	(31)	24
Net cash used in operating activities	(3,872)	(6,251)
Investing Activities:
Purchases of property and equipment	(630)	(292)
Proceeds from disposal of fixed assets	282
Purchases of debt securities	(11,692)
Proceeds from sales of debt securities	205
Net cash used in investing activities	(11,835)	(292)
Financing Activities:
Proceeds from exercise of stock options	21	463
Net cash provided by financing activities	21	463
Net decrease in cash, cash equivalents, and restricted cash	(15,686)	(6,080)
Cash, cash equivalents, and restricted cash at beginning of period	35,234	41,314
Cash, cash equivalents, and restricted cash at end of period	19,548	35,234
Supplemental Schedule of Non-Cash Financing Activities:
Accrued capital expenditures		$ 2