Condensed Consolidated Balance Sheets (Unaudited) $ in Thousands, $ in Millions	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Current assets:
Cash and cash equivalents	$ 87,427	$ 106,029
Restricted cash	10	10
Available-for-sale securities	51,090	37,972
Receivable from collaboration partner - related party	4,586	1,816
Research and development tax incentive receivable	1,155	1,347
Prepaid expenses and other current assets	3,234	3,773
Total current assets	147,502	150,947
Property and equipment, net	904	879
Restricted cash - noncurrent	450	450
Available-for-sale securities - noncurrent		11,458
Total assets	148,856	163,734
Current liabilities:
Accounts payable	4,871	1,257
Payable to collaboration partner - related party	764
Accrued expenses and other payables	10,496	9,546
Deferred revenue - related party	7,970	31,752
Total current liabilities	24,101	42,555
Deferred rent - noncurrent	797	547
Total liabilities	24,898	43,102
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; 24,138,102 and 21,088,306 shares issued and outstanding as of September 30, 2018 and December 31, 2017, respectively
Additional paid-in capital	250,670	222,188
Accumulated other comprehensive loss	(103)	(6)
Accumulated deficit	(126,609)	(101,550)
Total stockholders equity	123,958	120,632
Total liabilities and stockholders equity	$ 148,856	$ 163,734