Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Elimination of limitation in net operating losses deductions as percentage of current year taxable income, percentage		80.00%
Recovery period on qualified improvement of property		15 years
Current income tax benefit	$ 13,407,000	$ 5,240,000	$ (2,288,000)
Amortization Period	5 years
Federal statutory income tax rate, percent	21.00%
Increase (decrease) in valuation allowance	$ (32,200,000)	45,400,000
Research and development and orphan drug tax credit carryforwards	45,576,000	47,970,000
Net of unrecognized tax benefits	$ 100,000	$ 100,000	100,000
Tax credit carryforwards, expiration year	2035	2041
Reserve for uncertain tax positions placed against credit carryforwards	$ 100,000	$ 100,000	100,000
Reserve for uncertain tax positions placed against qualified expenses	$ 0	0	0
Unrecognized tax benefits period	12 months
Cumulative changes in ownership Interest percentage threshold, subject to annual limitation of NOL and tax credit carryforwards	50.00%
Ownership interest change period	3 years
Domestic Country [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards		0	44,700,000
Operating Loss Carryforwards Expiration Year	2034
Research and development and orphan drug tax credit carryforwards		45,600,000	48,000,000.0
U. S State Tax Authority [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards		59,900,000	$ 79,700,000
Operating Loss Carryforwards Expiration Year	2041
2018 Tax Year [Member]
Income Tax Disclosure [Line Items]
Current income tax benefit		$ (500,000)