Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (4,297)	$ (4,766)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	525	247
Stock-based compensation	547	696
Change in value of warrant liabilities, (gain) loss	(8)	889
Changes in operating assets and liabilities:
Trade accounts receivable	93	64
Inventory	(198)	(368)
Prepaid expenses and other current assets	117	169
Other assets		22
Accounts payable and accrued liabilities	(155)	(1,127)
Deferred revenue	(7)	25
Net cash used in operating activities	(3,383)	(4,149)
Investing Activities:
Purchases of property and equipment	(71)	(10,183)
Net cash used in investing activities	(71)	(10,183)
Financing Activities:
Proceeds from exercise of stock options	47	426
Proceeds from stock issuance		414
Net cash provided by financing activities	47	840
Net decrease in cash and cash equivalents and restricted cash	(3,407)	(13,492)
Cash and cash equivalents and restricted cash at beginning of period	41,314	58,896
Cash and cash equivalents and restricted cash at end of period	37,907	45,404
Supplemental Schedule of Non-Cash Investing and Financing Activities:
Cashless exercise of warrants		975
Accrued capital expenditures		$ 11