v3.24.0.1
Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2017
Income Taxes [Line Items]        
Income tax benefit (provision) $ 677,000 $ (681,000)    
Net operating loss carryforwards 54,700,000      
Net operating loss carryovers 172,547,000 158,413,000    
Capitalized research and development deferred tax assets 41,239,000 36,643,000    
Increase in valuation allowance 20,900,000      
Gross unrecognized tax benefit 15,790,000 13,945,000 $ 19,864,000  
Unrecognized tax benefit that could affect annual effective tax rate if recognized 0      
Subsidiaries Outside of Singapore [Member]        
Income Taxes [Line Items]        
Cash held by subsidiaries 23,900,000 44,100,000    
Japan [Member]        
Income Taxes [Line Items]        
Net operating loss carryovers $ 1,400,000 2,300,000    
Operating loss carryforwards expiration year 2024      
Tax years open to examination 2018      
Singapore [Member]        
Income Taxes [Line Items]        
Net operating loss carryovers $ 122,000,000 111,200,000    
Tax years open to examination 2019      
UK [Member]        
Income Taxes [Line Items]        
Net operating loss carryovers $ 335,700,000 314,500,000    
Tax years open to examination 2022      
United States [Member]        
Income Taxes [Line Items]        
Tax years open to examination 2020      
Federal [Member]        
Income Taxes [Line Items]        
Net operating loss carryforwards $ 302,200,000      
Net operating loss carryforwards available to offset future income tax liabilities indefinitely $ 301,400,000      
Net operating loss carryforwards available to offset future income tax liabilities       $ 800,000
Operating Loss Carry forward expiration year 2037      
Federal [Member] | Research and development        
Income Taxes [Line Items]        
Tax credit carryforward $ 6,100,000      
Research and development tax credit carryforward expiration year 2042      
Federal [Member] | Orphan Drug Credits [Member]        
Income Taxes [Line Items]        
Tax credit carryforward $ 0      
State [Member]        
Income Taxes [Line Items]        
Operating Loss Carry forward expiration year 2038      
State [Member] | Research and development        
Income Taxes [Line Items]        
Tax credit carryforward $ 2,600,000 200,000    
Research and development tax credit carryforward expiration year 2037      
U.S. Tax Guidance relating to Capitalization of Research and Development Expenditures [Member]        
Income Taxes [Line Items]        
Income tax benefit (provision) $ 700,000 $ (700,000)