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Cash and Cash Equivalents (Excluding Overdrafts) - Additional Information (Detail)
Dec. 31, 2019
Dec. 31, 2018
US Dollars [member]    
Cash and cash equivalents [line items]    
Cash and cash equivalents currency split 30.00% 18.00%
Sterling [member]    
Cash and cash equivalents [line items]    
Cash and cash equivalents currency split 12.00% 30.00%
Other currency [member]    
Cash and cash equivalents [line items]    
Cash and cash equivalents currency split 58.00% 52.00%