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Defined Contribution Plan (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
United States      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Employer contributions $ 0 $ 0  
United Kingdom      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Percent contribution by employee salary     3.00%