Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 20,993	$ 16,966	$ 7,191	$ 7,888
Accounts receivable, net of allowances of $0 and $26, respectively	2,672	15
Costs and estimated earnings in excess of billings on uncompleted contracts	0	680
Inventory	4,505	4,541
Other current assets	1,221	1,015
Total current assets	29,391	23,217
Property and equipment, net	3,122	3,251
Restricted cash	435	435
Intangible assets	544	602
Other assets	2,498	2,262
Total assets	35,990	29,767
Current liabilities
Accounts payable	2,275	3,063
Accrued liabilities	6,155	5,864
Deferred revenue	5,000	0
Billings on uncompleted contracts in excess of related costs	446	5
Other current liabilities	10,063	10,142
Total current liabilities	23,939	19,074
Deferred revenue, net of current portion		0
Deferred rent, net of current portion	416	302
Other long-term liabilities	21	305
Total liabilities	24,376	19,681
Commitments and contingencies (Note 8)
Shareholders' equity
Preferred stock, par value $0.001; 25,000 shares authorized; 0 and 0 shares issued and outstanding	0	0
Common stock, par value $0.001; 150,000 shares authorized; 93,073 and 78,597 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	93	79
Additional paid-in capital	545,978	528,873
Accumulated deficit	(534,457)	(518,866)
Total shareholders' equity	11,614	10,086
Total liabilities and shareholders' equity	35,990	29,767
Reconciliation of cash, cash equivalents, and restricted cash balances
Cash and cash equivalents	20,993	16,966	$ 7,191	$ 7,888
Restricted cash	435	435
Cash, cash equivalents, and restricted cash	$ 21,428	$ 17,401