Income Taxes - Summary of Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax benefit at statutory rate	$ (8,242)	$ (5,008)
State income tax, net of federal benefit	(3,783)	(1,593)
Permanent items	16	3
Fair value adjustments	0	15
Non-deductible interest expense	0	706
Stock-based compensation	56	45
Orphan drug credit	(925)	(475)
Research and development credits	(763)	(274)
Uncertain tax positions	548	222
Tax Cuts and Jobs Act	0	(15)
Change in state rate	(34)	0
Change in valuation allowance	13,179	6,426
Other	(52)	(52)
Income tax expense (benefit)	$ 0	$ 0