Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net loss	$ (5,647)	$ (3,556)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	85	187
Amortization of intangible assets	29	32
Share-based compensation expense	310	300
Inventory write-downs	0	122
Other non-cash adjustments	(16)	1
Change in:
Accounts receivable, net	85	691
Costs and estimated earnings in excess of billings on uncompleted contracts	(184)	0
Inventory	(819)	(166)
Other current and non-current assets	(271)	48
Accounts payable	(320)	141
Accrued liabilities	315	383
Deferred revenue	(247)	(1,165)
Billings on uncompleted contracts in excess of related costs	(41)	0
Other long-term liabilities	(8)	0
Net cash used in operating activities	(6,729)	(2,982)
Cash flows from investing activities
Purchases of property and equipment	(755)	(82)
Net cash used in investing activities	(755)	(82)
Cash flows from financing activities
Net proceeds from issuance of common stock and warrants	0	6,385
Net cash provided by financing activities	0	6,385
Change in cash and cash equivalents	(7,484)	3,321
Cash and cash equivalents, at beginning of period	15,139	7,888
Cash and cash equivalents, at end of period	7,655	11,209
Supplemental schedule of non-cash investing and financing activities
Non-cash additions to property and equipment	$ 713	$ 154