Income Taxes - Additional Information (Details) - USD ($)		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
U.S. corporate tax rate	21.00%	21.00%	34.00%
Income tax expense		$ 0	$ 0
Increase in valuation allowance due to deferred tax assets		25,100,000	7,700,000
Uncertain tax positions		0
Income tax expense, interest or penalties		0	$ 0
Orphan Drug
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 7,300,000
Tax credit carryforwards expiration year		2038
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 52,400,000
Net operating loss carryforwards indefinitely		21,300,000
Federal | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards		2,500,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		46,600,000
State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 3,500,000
Federal and State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards expiration year		2038
Federal and State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards expiration year		2038