Condensed Consolidated Balance Sheets (Unaudited) $ in Thousands, $ in Millions	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Current assets:
Cash and cash equivalents	$ 69,577	$ 106,029
Restricted cash	10	10
Available-for-sale securities	65,383	37,972
Receivable from collaboration partner - related party	2,722	1,816
Research and development tax incentive receivable	1,918	1,347
Prepaid expenses and other current assets	2,621	3,773
Total current assets	142,231	150,947
Property and equipment, net	1,001	879
Restricted cash - noncurrent	450	450
Available-for-sale securities - noncurrent	5,557	11,458
Total assets	149,239	163,734
Current liabilities:
Accounts payable	1,307	1,257
Payable to collaboration partner - related party	379
Accrued expenses and other payables	10,358	9,546
Deferred revenue - related party	21,880	31,752
Total current liabilities	33,924	42,555
Deferred rent - noncurrent	694	547
Total liabilities	34,618	43,102
Commitments and contingencies (Note 8)
Stockholders equity:
Additional paid-in capital	223,904	222,188
Accumulated other comprehensive loss	(72)	(6)
Accumulated deficit	(109,211)	(101,550)
Total stockholders equity	114,621	120,632
Total liabilities and stockholders equity	$ 149,239	$ 163,734