Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 6,499	$ 5,759
Short-term investments	14,962	20,035
Accounts receivable	2,842	5,063
Prepaid expenses and other current assets	1,219	1,397
Total current assets	25,522	32,254
Long-term investments	5,561	1,995
Materials inventory	2,970	3,357
Property and equipment, net	8,629	10,964
Intangible assets, net	3,209	4,001
Other assets	587	597
Total assets	46,478	53,168
Current liabilities:
Accounts payable	1,024	309
Accrued liabilities	1,138	1,451
Accrued compensation and employee benefits	2,167	1,663
Deferred revenue	1,745	1,533
Total current liabilities	6,074	4,956
Deferred rent	3,049	3,149
Other long-term liabilities	55	67
Total liabilities	9,178	8,172
Commitments and contingencies (note 5)
Stockholders’ equity:
Common stock, par value $0.001 per share—200,000,000 shares authorized; 49,559,701 and 49,513,528 shares issued and outstanding as of June 30, 2017 and December 31, 2016, respectively	50	50
Additional paid-in capital	214,295	213,313
Accumulated other comprehensive loss	(21)	(32)
Accumulated deficit	(177,024)	(168,335)
Total stockholders’ equity	37,300	44,996
Total liabilities and stockholders’ equity	$ 46,478	$ 53,168