Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue:
Total revenue	$ 5,062		$ 7,936	$ 911
Operating expenses:
Research and development	22,303	$ 9,151	52,732	36,948
General and administrative	3,227	3,805	10,609	8,877
Total operating expenses	25,530	12,956	63,341	45,825
Operating loss	(20,468)	(12,956)	(55,405)	(44,914)
Other income	1,002	367	1,780	788
Loss before benefit from income taxes	(19,466)	(12,589)	(53,625)	(44,126)
Benefit from income taxes	66	145	264	178
Net loss	$ (19,400)	$ (12,444)	$ (53,361)	$ (43,948)
Net loss per share:
Basic and Diluted	$ (0.51)	$ (0.38)	$ (1.54)	$ (1.43)
Weighted average shares:
Basic and Diluted	38,034,216	32,591,550	34,696,835	30,729,752
Other comprehensive income (loss), net of tax of $0:
Change in unrealized gains (losses) on available-for- sale marketable securities	$ 70	$ 53	$ 83	$ 37
Total comprehensive loss	(19,330)	$ (12,391)	(53,278)	(43,911)
License and Milestone Fees [Member]
Revenue:
Total revenue	5,029		7,903	530
Collaborative Revenue [Member]
Revenue:
Total revenue				313
Clinical Compound Revenue [Member]
Revenue:
Total revenue	$ 33		$ 33	$ 68