Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

v3.21.1
Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
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 2040. The federal research and development and federal orphan drug tax credit carryforwards expire 2021 through 2040, and the state tax credit will carry forward indefinitely.      
Provision for income taxes $ 0 $ 0    
Net valuation allowance increase (decrease) $ 17,200 $ 23,600    
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 all years remain open for income tax examination by tax authorities      
Domestic Tax Authority [Member]        
Income Tax [Line Items]        
Federal net operating loss $ 490,400      
Net operating loss carryforward 490,400      
Research and development tax credit carry forwards 21,400      
Domestic Tax Authority [Member] | Orphan Drug [Member]        
Income Tax [Line Items]        
Research and development tax credit carry forwards $ 10,100      
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 $ 288,600      
Net operating loss carryforward 288,600      
Research and development tax credit carry forwards $ 5,800      
State and Local Jurisdiction [Member] | Federal [member]        
Income Tax [Line Items]        
Federal net operating loss     $ 234,700 $ 255,700
Net operating loss carryforward     $ 234,700 $ 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 2040