Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Total revenue	$ 2,874		$ 2,874	$ 911
Operating expenses:
Research and development	17,002	$ 6,961	30,429	27,797
General and administrative	3,685	2,672	7,382	5,072
Total operating expenses	20,687	9,633	37,811	32,869
Operating loss	(17,813)	(9,633)	(34,937)	(31,958)
Other income	467	331	778	421
Loss before benefit from income taxes	(17,346)	(9,302)	(34,159)	(31,537)
Benefit from income taxes	152	2	198	33
Net loss	$ (17,194)	$ (9,300)	$ (33,961)	$ (31,504)
Net loss per share:
Basic and Diluted	$ (0.52)	$ (0.29)	$ (1.03)	$ (1.06)
Weighted average shares:
Basic and Diluted	33,315,809	32,239,877	33,000,487	29,783,424
Other comprehensive income (loss), net of tax of $0:
Change in unrealized gains (losses) on available-for- sale marketable securities	$ 57	$ (37)	$ 13	$ (16)
Total comprehensive loss	(17,137)	$ (9,337)	(33,948)	(31,520)
License and Milestone Fees [Member]
Revenue:
Total revenue	$ 2,874		$ 2,874	530
Collaborative Revenue [Member]
Revenue:
Total revenue				313
Clinical Compound Revenue [Member]
Revenue:
Total revenue				$ 68