Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 13,469	$ 911	$ 86
Operating expenses:
Research and development	75,531	48,524	49,253
General and administrative	15,320	11,872	9,233
Total operating expenses	90,851	60,396	58,486
Operating loss	(77,382)	(59,485)	(58,400)
Other income	2,980	1,156	652
Loss before benefit from income taxes	(74,402)	(58,329)	(57,748)
Benefit from income taxes	389	204	468
Net loss	$ (74,013)	$ (58,125)	$ (57,280)
Net loss per share:
Basic and Diluted	$ (2.06)	$ (1.86)	$ (2.10)
Weighted average shares:
Basic and Diluted	35,892,786	31,202,842	27,279,008
Other comprehensive income (loss), net of tax of $0:
Change in unrealized gains (losses) on available for sale marketable securities	$ (44)	$ (73)	$ 38
Total comprehensive loss	(74,057)	(58,198)	(57,242)
License and Milestone Fees [Member]
Revenue:
Total revenue	13,436	530
Collaborative Revenue [Member]
Revenue:
Total revenue		313
Clinical Compound Revenue [Member]
Revenue:
Total revenue	$ 33	$ 68	$ 86