Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Current tax expense	$ 0
Deferred tax expense	0
Federal operating loss carryforwards	$ 1,300,000,000
Federal net operating loss carryforwards, limitation percentage	80.00%
Federal orphan drug tax credit carry forwards	$ 40,100,000
Tax credit carry forwards expiration period	2034
Change in amount of deferred tax assets	$ 94,500,000
Valuation allowance	470,604,000	$ 376,103,000
Valuation allowance, increase (decrease), amount	94,500,000	(107,200,000)	$ 174,900,000
Gross unrecognized tax benefits	6,084,000	0	0
Accrued interest or penalties related to uncertain tax positions	0	0
Uncertain tax positions	0	$ 0	$ 0
Begin to Expire 2033 [Member]
Income Tax Disclosure [Line Items]
Federal operating loss carryforwards	$ 30,200,000
Federal net operating loss carryforwards expiration year	2033
Begin to Expire 2028 [Member]
Income Tax Disclosure [Line Items]
State operating loss carryforwards	$ 584,800,000
State net operating loss carryforwards expiration year	2031
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Research and development tax credits carryforwards	$ 56,900,000
Research and development tax credits carryforwards expiration year	2031
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Research and development tax credits carryforwards	$ 11,600,000
Research and development tax credits carryforwards expiration year	2028