Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Income tax benefit	$ 0	$ 0	$ 0
Unrecognized tax benefits	0	$ 0
Massachusetts [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 394,100,000
Net operating loss carry forwards, expiration year, start	2035
Future Tax Years [Member] | Maximum [Member]
Income Tax Disclosure [Line Items]
Taxable income on NOL	80.00%
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 402,500,000
Federal [Member] | Before 2018 [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 119,800,000
Net operating loss carry forwards, expiration year, start	2035
Federal [Member] | After 2017 [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 282,700,000
Federal [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 43,700,000
Tax credit carryforwards, expiration year, start	2031
Federal [Member] | Orphan Drug Credit Carryforwards [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 23,700,000
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	394,100,000
State [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 11,900,000
Tax credit carryforwards, expiration year, start	2028