Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Provision or benefit from income taxes		$ 0	$ 0	$ 0
Decrease in net deferred assets		7,869,000
Net operating loss carryforwards		58,000,000	36,100,000
Unrecognized tax benefit		$ 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		$ 2,700,000	9,400,000	$ 3,900,000
Federal
Income Taxes [Line Items]
Tax credit carryforwards		5,600,000	3,300,000
State
Income Taxes [Line Items]
Tax credit carryforwards		1,000,000	$ 612,000
PATH Act of 2015
Income Taxes [Line Items]
Converted research tax credit to offset payroll tax liabilities		500,000
PATH Act of 2015 | Prepaid Expenses and Other Current Assets
Income Taxes [Line Items]
Converted research tax credit to offset payroll tax liabilities		416,000
PATH Act of 2015 | Other Non-current Assets
Income Taxes [Line Items]
Converted research tax credit to offset payroll tax liabilities		$ 84,000
Scenario Forecast
Income Taxes [Line Items]
Corporate income tax rates	21.00%
Orphan drug credit of qualifying expenditures percentage	25.00%
Maximum
Income Taxes [Line Items]
Corporate income tax rates		35.00%
Orphan drug credit of qualifying expenditures percentage		50.00%