Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Orphan drug tax credit carryforwards	$ 20,096,000	$ 18,778,000	$ 18,100,000
Valuation allowance	167,424,000	160,987,000
Increase (decrease) in valuation allowance	(6,400,000)	1,200,000
Unrecognized tax benefits	0	0
Uncertain tax position	0
Federal
Income Taxes [Line Items]
Net operating loss	58,400,000	52,800,000	52,800,000
Federal | Research and experimentation
Income Taxes [Line Items]
Research and experimentation credit carryforwards	11,300,000	11,400,000	11,900,000
State
Income Taxes [Line Items]
Net operating loss	10,400,000	8,000,000.0	5,900,000
State | Research and experimentation
Income Taxes [Line Items]
Research and experimentation credit carryforwards	$ 3,500,000	$ 3,500,000	$ 3,500,000