Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 106,029	$ 21,084
Restricted cash - current	10	10
Available-for-sale securities - current	37,972	56,515
Receivable from collaboration partner - related party	1,816
Research and development tax incentive receivable	1,347	2,241
Prepaid expenses and other current assets	3,773	3,394
Total current assets	150,947	83,244
Property and equipment, net	879	562
Restricted cash - noncurrent	450
Available-for-sale securities - noncurrent	11,458	10,150
Other assets		34
Total assets	163,734	93,990
Current liabilities:
Accounts payable	1,257	1,163
Accrued expenses and other payables	9,546	5,272
Deferred revenue - related party	31,752
Total current liabilities	42,555	6,435
Deferred rent - noncurrent	547
Total liabilities	43,102	6,435
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.00001 par value, 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.00001 par value, 90,000,000 shares authorized; 21,088,306 and 16,722,280 shares issued and outstanding as of December 31, 2017 and 2016, respectively	0	0
Additional paid-in capital	222,188	152,393
Accumulated other comprehensive loss	(6)	(245)
Accumulated deficit	(101,550)	(64,593)
Total stockholders' equity	120,632	87,555
Total liabilities and stockholders' equity	$ 163,734	$ 93,990