Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 61,135	$ 48,475
Short-term investments	80,321	115,318
Receivables from collaborations	1,809	1,142
Prepaid expenses and other current assets	1,553	2,732
Total current assets	144,818	167,667
Long-term investments		22,361
Other assets	845	228
Restricted cash	440	440
Property and equipment, net	1,571	1,759
Total assets	147,674	192,455
Current liabilities:
Accounts payable	517	1,072
Accrued liabilities	10,088	8,938
Current portion of deferred revenue		29,017
Total current liabilities	10,605	39,027
Deferred revenue, less current portion		2,028
Deferred rent	1,159	1,093
Total liabilities	11,764	42,148
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.0001 par value, 200,000 shares authorized as of September 30, 2018 and December 31, 2017; 37,204 and 35,759 shares issued and outstanding as of September 30, 2018 and December 31, 2017, respectively	4	4
Additional paid-in capital	312,751	300,906
Accumulated deficit	(176,671)	(150,333)
Accumulated other comprehensive loss	(174)	(270)
Total stockholders’ equity	135,910	150,307
Total liabilities and stock and stockholders’ equity	$ 147,674	$ 192,455