Annual report pursuant to Section 13 and 15(d)

Income taxes - Change in Tax Rate (Details)

v3.20.4
Income taxes - Change in Tax Rate (Details)
12 Months Ended 24 Months Ended 36 Months Ended
Apr. 01, 2020
Mar. 31, 2020
Dec. 31, 2020
USD ($)
Dec. 31, 2020
GBP (£)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Income taxes                
Net operating loss     $ (133,405,000)   $ (139,770,000) $ (82,365,000)    
Annual allowance | £       £ 5,000,000        
Percentage on taxable profit     50.00%       50.00% 50.00%
Her Majesty's Revenue and Customs (HMRC)                
Income taxes                
Tax rate (as a percent) 19.00% 17.00% 19.00% 19.00% 19.00% 19.00%   21.00%
Operating Loss Carryforwards     $ 334,400,000       $ 334,400,000 $ 334,400,000
Expenditure credit carryforward     700,000       $ 700,000 700,000
Increase in net deferred tax asset and corresponding valuation allowance     $ 5,675,000          
Her Majesty's Revenue and Customs (HMRC) | U.K.                
Income taxes                
Tax rate, deferred taxes (as a percent)     19.00% 19.00% 17.00%      
Her Majesty's Revenue and Customs (HMRC) | U.S.                
Income taxes                
Tax rate, deferred taxes (as a percent)     21.00% 21.00%        
Internal Revenue Service (IRS)                
Income taxes                
Tax rate, deferred taxes (as a percent)             21.00%  
Tax credit carryforwards     $ 7,500,000       $ 7,500,000 $ 7,500,000
Tax credit carried forward period     20 years 20 years