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Employee benefits - Additional information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Level 3      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Transfers in or out between levels $ 0 $ 0  
Level 1 and Level 2      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Transfers in or out between levels 0 0  
Savings Plans      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Savings Plans 102,900,000 82,700,000  
Savings Plans Contributions $ 20,300,000 $ 18,700,000 $ 13,300,000
Savings Plans Stocks Held 1,253,702 1,246,519