Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 24,300	$ 31,219
Accounts receivable, net of allowances of $34 at March 31, 2018 and December 31, 2017	8,974	11,800
Inventories	1,212	1,036
Prepaid expenses and other current assets	1,481	984
Total current assets	35,967	45,039
Restricted cash	1,511	1,557
Marketable securities	697	671
Property and equipment, net	2,620	2,815
Goodwill	3,241	3,241
Other non-current assets	470	302
Total assets	44,506	53,625
Current liabilities:
Accounts payable	2,597	3,545
Accrued compensation	6,134	4,753
Other accrued liabilities	5,304	4,362
Deferred revenue	7,518	12,292
Total current liabilities	21,553	24,952
Deferred revenue, net of current portion	5,529	1,501
Lease incentive obligation, net of current portion	354	460
Financing obligation, net of current portion	243	302
Other long-term liabilities	1,759	1,863
Total liabilities	29,438	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; 48,925 shares and 48,365 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	5	5
Additional paid-in capital	339,354	340,079
Accumulated other comprehensive loss	0	(472)
Accumulated deficit	(324,291)	(315,065)
Total stockholders' equity	15,068	24,547
Total liabilities and stockholders' equity	$ 44,506	$ 53,625