Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 5,759	$ 11,676
Short-term investments	20,035	23,656
Accounts receivable, net of allowance for doubtful accounts of $0 as of December 31, 2016 and December 31, 2015	5,063	6,114
Prepaid expenses and other current assets	1,397	1,608
Total current assets	32,254	43,054
Long-term investments	1,995
Materials inventory	3,357	4,413
Property and equipment, net	10,964	15,735
Intangible assets, net	4,001	5,969
Other assets	597	506
Total assets	53,168	69,677
Current liabilities:
Accounts payable	309	848
Accrued liabilities	1,451	2,385
Accrued compensation and employee benefits	1,663	4,416
Deferred revenue	1,533	2,595
Total current liabilities	4,956	10,244
Deferred rent, net of current portion	3,149	3,299
Other long-term liabilities	67	35
Total liabilities	8,172	13,578
Commitments and contingencies (note 5)
Stockholders’ equity:
Common stock, par value $0.001 per share—200,000,000 shares authorized; 49,513,528 and 49,092,260 shares issued and outstanding as of December 31, 2016 and December 31, 2015, respectively	50	49
Additional paid-in capital	213,313	208,972
Accumulated other comprehensive loss	(32)	(24)
Accumulated deficit	(168,335)	(152,898)
Total stockholders’ equity	44,996	56,099
Total liabilities and stockholders’ equity	$ 53,168	$ 69,677