Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 246,122	$ 224,571
Short-term investments	68,564	31,933
Receivable from collaboration partner		1,013
Prepaid expenses and other current assets	4,760	1,876
Total current assets	319,446	259,393
Property and equipment, net	5,138	3,147
Long-term investments	80,148	19,900
Restricted cash and other	2,521	368
Total assets	407,253	282,808
Current liabilities
Accounts payable	2,946	2,301
Accrued liabilities	20,758	11,639
Prepayment from collaboration partner	12,973	4,432
Deferred revenue		33,558
Total current liabilities	36,677	51,930
Other long-term liabilities	9	202
Total liabilities	36,686	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 shares authorized at December 31, 2018 and 2017; 40,288,949 and 35,812,791 shares issued and outstanding at December 31, 2018 and 2017, respectively	4	4
Additional paid-in capital	573,183	365,719
Accumulated other comprehensive loss	(67)	(192)
Accumulated deficit	(202,553)	(134,855)
Total stockholders’ equity	370,567	230,676
Total liabilities and stockholders’ equity	$ 407,253	$ 282,808