Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Income tax expense	$ (3,000)	$ (14,000)
Federal orphan drug credits	$ 122,700,000
Federal orphan drug credits begin to expire	2031
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 294,800,000
Net operating loss carryforwards expire year begin	2033
State [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 20,300,000
Tax credit carryforwards expire year begin	2022
Tax credit carryforwards expire year through	2025
State [Member] | Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 100,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 209,500,000
Net operating loss carryforwards expire year begin	2033
Federal [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 28,800,000
Tax credit carryforwards expire year begin	2022
Tax credit carryforwards expire year through	2025
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Income tax expense	$ 100,000	$ 100,000