Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jun. 30, 2021	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Description of net operating loss carryforwards, expire period	The state net operating loss carryforwards will expire beginning in 2028 through 2041. The federal research and development and federal orphan drug tax credit carryforwards expire 2021 through 2041, and the state tax credit will carry forward indefinitely.
Provision for income taxes	$ 0	$ 0
Net valuation allowance increase (decrease)	$ 14,700	$ 17,200
Cumulative change in ownership	50.00%
Cumulative change in ownership period	3 years
Significant change to its unrecognized tax benefits over the next twelve months	$ 0
Income tax examination years	the tax years 2001 to 2021 remain open for income tax examination by tax authorities
Maximum Threshold On Tax Credit Offset			$ 5,000
Average Taxable Income Fixed For Suspension Of Use Of Net Operating Losses			1,000
Minimum Taxable Income Fixed For Suspension Of Tax Credit Offset			$ 5,000
Minimum [Member]
Income Tax [Line Items]
Open tax year	2001
Maximum [Member]
Income Tax [Line Items]
Open tax year	2021
Domestic Tax Authority [Member]
Income Tax [Line Items]
Federal net operating loss	$ 522,700
Net operating loss carryforward	522,700
Research and development tax credit carry forwards	24,800
Domestic Tax Authority [Member] | Orphan Drug [Member]
Income Tax [Line Items]
Research and development tax credit carry forwards	$ 10,200
Domestic Tax Authority [Member] | Minimum [Member]
Income Tax [Line Items]
NOL carry forward expiry date	2024
Domestic Tax Authority [Member] | Maximum [Member]
Income Tax [Line Items]
NOL carry forward expiry date		2037
State and Local Jurisdiction [Member]
Income Tax [Line Items]
Federal net operating loss	$ 288,300
Net operating loss carryforward	288,300
Research and development tax credit carry forwards	$ 6,200
State and Local Jurisdiction [Member] | Federal [member]
Income Tax [Line Items]
Federal net operating loss				$ 267,000	$ 255,700
Net operating loss carryforward				$ 267,000	$ 255,700
State and Local Jurisdiction [Member] | Minimum [Member] | Federal [member]
Income Tax [Line Items]
NOL carry forward expiry date	2028
State and Local Jurisdiction [Member] | Maximum [Member] | Federal [member]
Income Tax [Line Items]
NOL carry forward expiry date	2041