Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 53,621	$ 31,219
Accounts receivable, net of allowances of $34 at June 30, 2018 and December 31, 2017	9,910	11,800
Inventories, net	1,036	1,036
Prepaid expenses and other current assets	1,162	984
Contract assets	554	0
Total current assets	66,283	45,039
Restricted cash	1,460	1,557
Marketable securities	676	671
Property and equipment, net	3,883	2,815
Goodwill	3,241	3,241
Other non-current assets	414	302
Total assets	75,957	53,625
Current liabilities:
Accounts payable	3,082	3,545
Accrued compensation	3,817	4,753
Other accrued liabilities	5,051	4,362
Deferred revenue	4,460	12,292
Total current liabilities	16,410	24,952
Deferred revenue, net of current portion	4,994	1,501
Lease incentive obligation, net of current portion	248	460
Financing obligation, net of current portion	183	302
Other long-term liabilities	1,592	1,863
Total liabilities	23,427	29,078
Commitments and Contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.0001 par value per share; 5,000 shares authorized; none issued and outstanding	0	0
Common stock, $0.0001 par value per share; 100,000 shares authorized; 53,508 shares and 48,365 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	5	5
Additional paid-in capital	380,551	340,079
Accumulated other comprehensive loss	0	(472)
Accumulated deficit	(328,026)	(315,065)
Total stockholders' equity	52,530	24,547
Total liabilities and stockholders' equity	$ 75,957	$ 53,625