Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Research premium and grant revenue	$ 5,319	$ 6,482	$ 3,767
Operating expenses:
Research and development	(49,615)	(47,994)	(23,604)
General and administrative	(29,472)	(13,535)	(7,921)
Total operating expenses	(79,087)	(61,529)	(31,525)
Loss from operations	(73,768)	(55,047)	(27,758)
Other income (expense):
Other income (expense), net	492	(783)	2,427
Interest income	318	343	14
Interest expense	(43)	(75)	(22,092)
Loss before income taxes	(73,001)	(55,562)	(47,409)
Income tax (expense) benefit	(1,355)	672	445
Net loss	(74,356)	(54,890)	(46,964)
Other comprehensive income (loss), net of tax
Exchange differences on translating foreign operations			2,026
Unrealized losses on available-for-sale financial assets	(26)	(18)	(68)
Reclassification to net income	43	68
Other comprehensive income, net of tax	17	50	1,958
Comprehensive loss	$ (74,339)	$ (54,840)	$ (45,006)
Loss per share
Basic and diluted (in dollars per share)	$ (2.49)	$ (2.56)	$ (4.80)
Weighted average number of shares:
Basic and diluted (in shares)	29,830,669	21,478,320	10,583,950