Annual report pursuant to Section 13 and 15(d)

Income taxes - Change in Tax Rate (Details)

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Income taxes - Change in Tax Rate (Details)
$ in Thousands, £ in Millions
12 Months Ended
Apr. 01, 2020
Apr. 01, 2017
Dec. 31, 2019
GBP (£)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Income taxes          
Net operating loss       $ (139,770) $ (82,365)
Annual allowance | £     £ 5    
Percentage on taxable profit       50.00%  
Her Majesty's Revenue and Customs (HMRC)          
Income taxes          
Tax rate (as a percent)   19.00% 19.00% 19.00% 19.00%
Tax rate, deferred taxes (as a percent)     17.00% 17.00%  
Operating Loss Carryforwards       $ 249,800  
Expenditure credit carryforward       $ 700  
Her Majesty's Revenue and Customs (HMRC) | Forecast          
Income taxes          
Tax rate (as a percent) 17.00%        
Internal Revenue Service (IRS)          
Income taxes          
Tax rate, deferred taxes (as a percent)     21.00% 21.00% 21.00%
Tax credit carryforwards       $ 5,700  
Tax credit carried forward period     20 years 20 years