Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Loss before income taxes	$ 39,200,000	$ 23,800,000
Deferred tax assets, valuation allowance	49,975,000	36,796,000
Deferred tax assets, increase (decrease) in valuation allowance	$ 13,200,000	(6,400,000)
Net operating losses and tax credit carryforwards limitations on change in ownership minimum percentage	50.00%
Net operating losses and tax credit carryforwards limitations on change in ownership period	3 years
Unrecognized tax benefits that would affect effective tax rate	$ 0
Unrecognized tax benefits	2,560,000	$ 1,809,000	$ 1,293,000
Federal
Income Taxes [Line Items]
Operating loss carryforwards available to offset future taxable income, amount	57,400,000
Federal | Tax Year 2018
Income Taxes [Line Items]
Net operating loss carryforwards	149,000,000
Federal | Tax Year 2018 | Research and Development
Income Taxes [Line Items]
Tax credit carryforwards, amount	$ 3,800,000
Tax credit carryforwards, expiration year	2028
Federal | Tax Year 2018 | Orphan Drug
Income Taxes [Line Items]
Tax credit carryforwards, amount	$ 4,200,000
Tax credit carryforwards, expiration year	2036
Federal | Maximum | Tax Year 2018
Income Taxes [Line Items]
Percentage of utilization net operating loss carryforwards to taxable income	80.00%
Federal | Maximum | Prior to 2018
Income Taxes [Line Items]
Percentage of utilization net operating loss carryforwards to taxable income	100.00%
Pennsylvania
Income Taxes [Line Items]
Percentage of utilization net operating loss carryforwards to taxable income	40.00%
Pennsylvania | Tax Year 2018
Income Taxes [Line Items]
Net operating loss carryforwards	$ 153,400,000
Percentage of utilization net operating loss carryforwards to taxable income	40.00%
Net operating loss carryforwards expiration beginning year	2029
Pennsylvania | Tax Year 2018 | Research and Development
Income Taxes [Line Items]
Tax credit carryforwards, amount	$ 400,000
Tax credit carryforwards, expiration year	2029