Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Loss before income taxes		$ 23,800,000	$ 10,200,000
Income tax expense (benefit)		0	0
Deferred tax assets, valuation allowance		36,796,000	30,370,000
Deferred tax assets, increase (decrease) in valuation allowance		$ 6,400,000	$ 7,100,000
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
U.S.federal corporate statutory tax rate		21.00%	35.00%
Adjustments made to the provisional amounts		$ 0
Reduction of deferred tax assets		11,000,000
Unrecognized tax benefits that would affect effective tax rate		0
Unrecognized tax benefits		1,809,000	$ 1,293,000	$ 1,067,000
Income tax penalties and interest accrued on uncertain tax positions		$ 0	$ 0
Federal
Income Taxes [Line Items]
Operating loss carryforwards, limitations on use, description		The federal NOLs generated prior to 2018 may be used to offset up to 100% of future taxable income and will begin to expire in 2022, unless previously utilized. The federal NOL generated in 2018 of $20.4 million will be available to offset up to 80% of future taxable income and may be carried forward indefinitely.
Operating loss carryforwards available to offset future taxable income, amount		$ 20,400,000
Tax years which remaining open for examination		2015 2016 2017 2018
Federal | 2018 Tax Year
Income Taxes [Line Items]
Net operating loss carryforwards		$ 111,900,000
Federal | 2018 Tax Year | Research and Development
Income Taxes [Line Items]
Tax credit carryforwards, amount		$ 3,200,000
Tax credit carryforwards, expiration year		2028
Federal | 2018 Tax Year | Orphan Drug
Income Taxes [Line Items]
Tax credit carryforwards, amount		$ 2,800,000
Tax credit carryforwards, expiration year		2036
Federal | Prior to 2018
Income Taxes [Line Items]
Net operating loss carryforwards expiration beginning year		2022
Federal | Maximum | 2018 Tax Year
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]
Operating loss carryforwards, limitations on use, description		The Pennsylvania NOLs may be used to offset 40% of future taxable income and will begin to expire in 2029, unless previously utilized.
Percentage of utilization net operating loss carryforwards to taxable income		35.00%
Tax years which remaining open for examination		2015 2016 2017 2018
Pennsylvania | Subsequent Event
Income Taxes [Line Items]
Percentage of utilization net operating loss carryforwards to taxable income	40.00%
Pennsylvania | 2018 Tax Year
Income Taxes [Line Items]
Net operating loss carryforwards		$ 105,900,000
Net operating loss carryforwards expiration beginning year		2029
Percentage of utilization net operating loss carryforwards to taxable income		40.00%
Pennsylvania | 2018 Tax Year | Research and Development
Income Taxes [Line Items]
Tax credit carryforwards, amount		$ 200,000
Tax credit carryforwards, expiration year		2029