Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (27,250)	$ (25,486)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation	1,722	1,141
Amortization of intangible assets	116	116
Share-based compensation expense	1,061	1,288
Inventory write-downs	4,414	1,004
Other non-cash adjustments	203	(42)
Change in:
Accounts receivable, net	(461)	230
Costs and estimated earnings in excess of billings on uncompleted contracts	(307)	(555)
Inventory	(982)	(4,312)
Other current and non-current assets	663	(2,314)
Accounts payable	(1,079)	1,147
Accrued liabilities	(374)	2,226
Billings in excess of costs and estimated earnings on uncompleted contracts	(5)	(138)
Other currrent liabilities	12	9,964
Other long-term liabilities	(305)	252
Net cash used in operating activities	(22,572)	(15,479)
Cash flows from investing activities
Proceeds on sale of property and equipment	0	59
Purchases of property and equipment	(1,118)	(3,100)
Net cash used in investing activities	(1,118)	(3,041)
Cash flows from financing activities
Principal payments under capital leases and long-term debt	(12)	0
Increase in deferred rent	139	0
Net proceeds from issuance of common stock and warrants	20,363	20,347
Net cash provided by financing activities	20,490	20,347
Change in cash and cash equivalents, and restricted cash	(3,200)	1,827
Cash, cash equivalents and restricted cash at beginning of period	17,401	15,574
Cash, cash equivalents and restricted cash at end of period	14,201	17,401
Supplemental schedule of non-cash investing and financing activities
Property and equipment acquired under capital leases	66	0
Non-cash additions to property and equipment	$ 445	$ 165