Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Income tax expense	$ 0	$ 0
Increase in valuation allowance due to deferred tax assets	40,200,000	25,100,000
Uncertain tax positions	0
Income tax expense, interest or penalties	0	$ 0
Orphan Drug
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 17,300,000
Tax credit carryforwards expiration year	2039
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 150,700,000
Net operating loss carryforwards indefinitely	119,600,000
Federal | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards	21,200,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	157,300,000
State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 5,200,000
Federal and State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards expiration year	2039
Federal and State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards expiration year	2039