Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Provision or benefit from income taxes	$ 0	$ 0	$ 0
Corporate income tax rates		21.00%
Orphan drug credit of qualifying expenditures percentage		25.00%
Effect of tax cuts and jobs act on income tax	0	$ 0	7,869,000
Net operating loss carryforwards	171,900,000	96,600,000
Net operating loss and tax credit carryforwards	58,400,000	10,900,000
Unrecognized tax benefit	$ 0	0
Earliest Tax Year
Income Taxes [Line Items]
Net operating loss carryforwards, expiration year	2033
Tax credit carryforwards, expiration year	2033
Tax Cuts and Jobs Act of 2017
Income Taxes [Line Items]
Increase in valuation allowance	$ 20,400,000	9,800,000	$ 2,700,000
Federal
Income Taxes [Line Items]
Tax credit carryforwards	10,900,000	7,300,000
State
Income Taxes [Line Items]
Tax credit carryforwards	$ 600,000	$ 400,000
Maximum
Income Taxes [Line Items]
Corporate income tax rates			35.00%
Orphan drug credit of qualifying expenditures percentage			50.00%