Annual report pursuant to Section 13 and 15(d)

Income taxes - Change in Tax Rate (Details)

v3.6.0.2
Income taxes - Change in Tax Rate (Details)
$ in Thousands, £ in Millions
6 Months Ended 12 Months Ended
Apr. 01, 2020
Apr. 01, 2017
Dec. 31, 2015
Dec. 31, 2016
GBP (£)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
Jun. 30, 2015
Jun. 30, 2014
Income taxes                
Effect of changes in tax rates on Consolidated statement of Operations (in dollars) | $         $ 0      
Percentage on taxable profit       50.00% 50.00%      
Operating Loss Carryforwards And Tax Credit Carryforward Annual Allowance | £       £ 5        
Her Majesty's Revenue and Customs (HMRC)                
Income taxes                
Tax rate (as a percent)     20.00% 20.00% 20.00%   20.75% 22.50%
Tax rate, deferred taxes (as a percent)       17.00% 17.00% 18.00%    
Her Majesty's Revenue and Customs (HMRC) | Forecast                
Income taxes                
Tax rate (as a percent) 17.00% 19.00%            
Internal Revenue Service (IRS)                
Income taxes                
Tax rate (as a percent)     34.00% 34.00% 34.00%   34.00% 34.00%
Tax rate, deferred taxes (as a percent)       34.00% 34.00% 40.00%