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Pension and other post-retirement benefits - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Employee Benefits Disclosure [Line Items]      
Defined contribution pension plan cost $ 12,126 $ 10,836  
Accumulated benefit obligation for pension plan 815,589 1,080,685  
Pension benefits      
Employee Benefits Disclosure [Line Items]      
Defined benefit plan, plan assets, amount 569,255 648,864 $ 629,157
Expected employer contributions for next year 22,386    
OPEB      
Employee Benefits Disclosure [Line Items]      
Defined benefit plan, plan assets, amount 172,167 192,375 $ 176,616
Expected employer contributions for next year 9,819    
Private Equity Funds | Level 3      
Employee Benefits Disclosure [Line Items]      
Defined benefit plan, plan assets, amount $ 21,904 $ 17,314