Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses:
Research and development	$ 10,860	$ 5,788	$ 45,489	$ 11,361
General and administrative	2,634	2,061	5,232	3,798
Total operating expenses	13,494	7,849	50,721	15,159
Loss from operations	(13,494)	(7,849)	(50,721)	(15,159)
Other income, net:
Interest income (expense), net	317	(5)	694	(5)
Other income	8	8	15	378
Net loss and comprehensive loss	(13,169)	(7,846)	(50,012)	(14,786)
Cumulative convertible preferred stock dividends	(3,291)	(1,050)	(6,332)	(1,878)
Net loss attributable to common stockholders	$ (16,460)	$ (8,896)	$ (56,344)	$ (16,664)
Net loss per share attributable to common stockholders, basic and diluted	$ (9.21)	$ (7.50)	$ (32.85)	$ (15.14)
Weighted average number of common shares used in net loss per share attributable to common stockholders, basic and diluted	1,787	1,186	1,715	1,101