Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (26,483)	$ (27,250)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation and amortization	1,649	1,838
Impairment of intangible assets	160	0
Impairment of property and equipment	434	0
Share-based compensation expense	1,569	1,061
Inventory write-downs	2,203	4,414
Other non-cash adjustments	0	203
Change in:
Accounts receivable, net	(603)	(461)
Costs and estimated earnings in excess of billings on uncompleted contracts	987	(307)
Inventory	(1,286)	(982)
Other current and non-current assets	1,911	663
Accounts payable	(268)	(1,079)
Accrued liabilities	(3,379)	(374)
Deferred revenue	21	0
Billings on uncompleted contracts in excess of related costs	0	(5)
Contract liabilities and other currrent liabilities	(316)	12
Operating lease liabilities	(642)	0
Other long-term liabilities	0	(305)
Net cash used in operating activities	(24,043)	(22,572)
Cash flows from investing activities
Purchases of property and equipment	(745)	(1,118)
Net cash used in investing activities	(745)	(1,118)
Cash flows from financing activities
Principal payments under finance leases	(20)	(12)
Increase in deferred rent	0	139
Net proceeds from issuance of common stock	16,879	20,363
Net cash provided by financing activities	16,859	20,490
Change in cash and cash equivalents, and restricted cash	(7,929)	(3,200)
Cash, cash equivalents and restricted cash at beginning of period	14,201	17,401
Cash, cash equivalents and restricted cash at end of period	6,272	14,201
Supplemental schedule of non-cash investing and financing activities
Property and equipment acquired under capital leases	0	66
Non-cash additions to property and equipment	37	445
Issuance of common stock for commitment fee	$ 535	$ 0