Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 19,886	$ 13,469	$ 911
Operating expenses:
Research and development	113,820	75,531	48,524
General and administrative	17,745	15,320	11,872
Total operating expenses	131,565	90,851	60,396
Operating loss	(111,679)	(77,382)	(59,485)
Other income	4,490	2,980	1,156
Loss before benefit from income taxes	(107,189)	(74,402)	(58,329)
Benefit from income taxes	816	389	204
Net loss	$ (106,373)	$ (74,013)	$ (58,125)
Net loss per share:
Basic and Diluted	$ (2.49)	$ (2.06)	$ (1.86)
Weighted average shares:
Basic and Diluted	42,669,333	35,892,786	31,202,842
Other comprehensive income (loss), net of tax of $0:
Change in unrealized gains (losses) on available-for-sale marketable securities	$ 284	$ (44)	$ (73)
Total comprehensive loss	(106,089)	(74,057)	(58,198)
License and Milestone Fees [Member]
Revenue:
Total revenue	19,746	13,436	530
Collaborative Revenue [Member]
Revenue:
Total revenue			313
Clinical Compound Revenue [Member]
Revenue:
Total revenue	$ 140	$ 33	$ 68