Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 346,827	$ 224,571
Short-term investments	51,766	31,933
Receivable from collaboration partner		1,013
Prepaid expenses and other current assets	2,604	1,876
Total current assets	401,197	259,393
Property and equipment, net	4,883	3,147
Long-term investments	27,648	19,900
Other long-term assets	426	368
Total assets	434,154	282,808
Current liabilities
Accounts payable	2,766	2,301
Accrued liabilities	13,553	11,639
Prepayment from collaboration partner	9,115	4,432
Deferred revenue	21,588	33,558
Total current liabilities	47,022	51,930
Other long-term liabilities	99	202
Total liabilities	47,121	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 June 30, 2018 and December 31, 2017, respectively; 40,049,160 and 35,812,791 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	4	4
Additional paid-in capital	558,376	365,719
Accumulated other comprehensive loss	(259)	(192)
Accumulated deficit	(171,088)	(134,855)
Total stockholders’ equity	387,033	230,676
Total liabilities and stockholders’ equity	$ 434,154	$ 282,808