Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 9,656	$ 5,319	$ 6,482
Operating expenses:
Research and development	(82,288)	(49,615)	(47,994)
General and administrative	(41,743)	(29,472)	(13,535)
Total operating expenses	(124,031)	(79,087)	(61,529)
Loss from operations	(114,375)	(73,768)	(55,047)
Other income (expense):
Other income (expense), net	(272)	492	(783)
Interest income	49	318	343
Interest expense	(133)	(43)	(75)
Loss before income taxes	(114,731)	(73,001)	(55,562)
Income tax (expense) benefit	(49)	(1,355)	672
Net loss	(114,780)	(74,356)	(54,890)
Other comprehensive income (loss), net of tax
Unrealized losses on available-for-sale securities		(26)	(18)
Reclassification to net income		(43)	(68)
Other comprehensive income, net of tax		17	50
Comprehensive loss	$ (114,780)	$ (74,339)	$ (54,840)
Loss per share
Basic and diluted (in dollars per share)	$ (2.26)	$ (2.49)	$ (2.56)
Weighted average number of shares:
Basic and diluted (in shares)	50,795,768	29,830,669	21,478,320
Collaboration revenue
Revenues:
Total revenues	$ 6,500
Research premium and grant revenue
Revenues:
Total revenues	$ 3,156	$ 5,319	$ 6,482