Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net loss	$ (24,243)	$ (16,472)	$ (14,542)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation	1,141	1,120	429
Amortization of intangible assets	116	127	128
Non-cash share-based compensation expense	1,288	1,223	1,007
Inventory write-downs	1,004	187	287
Other non-cash adjustments	(42)	27	(62)
Change in:
Accounts receivable, net	230	1,442	(1,018)
Costs and estimated earnings in excess of billings on uncompleted contracts	(555)	(125)	0
Inventory	(4,312)	(558)	(1,033)
Other current and non-current assets	(2,533)	(18)	(147)
Accounts payable	1,147	(174)	493
Accrued liabilities	2,226	245	572
Deferred revenue	(999)	(2,122)	8,271
Billings on uncompleted contracts in excess of related costs	(163)	168	(230)
Other current liabilities	9,964	56	18
Other long-term liabilities	252	53	0
Net cash used in operating activities	(15,479)	(14,821)	(5,827)
Cash flows from investing activities
Proceeds on sale of property and equipment	59	4	0
Purchases of property and equipment	(3,100)	(895)	(1,140)
Net cash used in investing activities	(3,041)	(891)	(1,140)
Cash flows from financing activities
Principal payments under capital leases and long-term debt	0	(15)	0
Net proceeds from issuance of common stock and warrants	20,347	22,978	6,506
Net cash provided by financing activities	20,347	22,963	6,506
Net increase (decrease) in cash and cash equivalents	1,827	7,251	(461)
Cash and cash equivalents, at beginning of period	15,139	7,888	8,349
Cash and cash equivalents, at end of period	16,966	15,139	7,888
Supplemental schedule of non-cash investing and financing activities
Non-cash additions to property and equipment	165	351	165
Issuance of common stock for commitment fee	$ 0	$ 721	$ 0