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Pension and other post-retirement benefits - Expected Benefit Payments (Detail)
$ in Thousands
Dec. 31, 2020
USD ($)
Pension Plans  
Defined Benefit Plan Disclosure [Line Items]  
2021 $ 46,858
2022 44,993
2023 46,358
2024 47,028
2025 48,197
2026—2030 241,151
Post-Employment Benefit Payments  
Defined Benefit Plan Disclosure [Line Items]  
2021 10,414
2022 11,033
2023 11,601
2024 12,165
2025 12,687
2026—2030 $ 68,826