Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 183,865	$ 224,571
Short-term investments	39,822	31,933
Receivable from collaboration partner		1,013
Prepaid expenses and other current assets	2,320	1,876
Total current assets	226,007	259,393
Property and equipment, net	4,030	3,147
Long-term investments	35,621	19,900
Other long-term assets	514	368
Total assets	266,172	282,808
Current liabilities
Accounts payable	2,292	2,301
Accrued liabilities	10,628	11,639
Prepayment from collaboration partner	7,701	4,432
Deferred revenue	28,227	33,558
Total current liabilities	48,848	51,930
Other long-term liabilities	151	202
Total liabilities	48,999	52,132
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; none issued and outstanding
Common stock, $0.0001 par value, 150,000,000 and 150,000,000 shares authorized at March 31, 2018 and December 31, 2017, respectively; 35,922,982 and 35,812,791 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	4	4
Additional paid-in capital	370,173	365,719
Accumulated other comprehensive loss	(329)	(192)
Accumulated deficit	(152,675)	(134,855)
Total stockholders’ equity	217,173	230,676
Total liabilities and stockholders’ equity	$ 266,172	$ 282,808