Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Expenses [Abstract]
Research and development	$ 30,163	$ 20,346	$ 17,066
General and administrative	17,640	8,739	5,181
Loss on transfer of nonfinancial assets	3,900	0	0
Total operating expenses	51,703	29,085	22,247
Loss from operations	(51,703)	(29,085)	(22,247)
Nonoperating Income (Expense) [Abstract]
Interest income	1,197	236	64
Interest expense	(2,147)	(720)	(490)
Change in fair value of preferred stock warrant liability	(288)	(3,398)	1,360
Change in fair value of derivative liability	183	(89)	(94)
Loss on preferred stock repurchase liability	0	0	(587)
Loss on extinguishment of debt	(566)	(229)	0
Other income	517	0	0
Total other income (expense), net	(1,104)	(4,200)	253
Net loss	(52,807)	(33,285)	(21,994)
Accruing dividends on Series A convertible preferred stock	(592)	(3,000)	(3,000)
Adjustment to accumulated deficit in connection with repurchase of Series Seed convertible preferred stock	0	(22)	0
Net loss attributable to common stockholders	$ (53,399)	$ (36,307)	$ (24,994)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (4.63)	$ (79.15)	$ (54.58)
Weighted average shares of common stock outstanding - basic and diluted (in shares)	11,530	459	458
Net loss	$ (52,807)	$ (33,285)	$ (21,994)
Currency translation adjustments	(119)	0	0
Total comprehensive loss	$ (52,926)	$ (33,285)	$ (21,994)