Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 3,816	$ 8,351
Short-term investments	23,613	22,098
Accounts receivable	2,451	3,349
Prepaid expenses and other current assets	952	936
Total current assets	30,832	34,734
Materials inventory	2,561	2,638
Property and equipment, net	3,125	3,432
Intangible assets, net	1,979	2,075
Right-of-use lease assets - operating	11,201
Other assets	509	514
Total assets	50,207	43,393
Current liabilities:
Accounts payable	193	760
Accrued liabilities	1,338	1,234
Accrued compensation and employee benefits	1,639	3,431
Current portion of lease obligation - operating	1,772
Deferred revenue	333	917
Total current liabilities	5,275	6,342
Deferred rent		2,667
Long term lease obligation - operating	12,307
Total liabilities	17,582	9,009
Commitments and contingencies (note 5)
Stockholders’ equity:
Common stock, par value $0.001 per share—200,000,000 shares authorized; 49,758,224 and 49,752,516 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively	50	50
Additional paid-in capital	216,502	216,034
Accumulated other comprehensive income (loss)	7	(27)
Accumulated deficit	(183,934)	(181,673)
Total stockholders’ equity	32,625	34,384
Total liabilities and stockholders’ equity	$ 50,207	$ 43,393