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Pension and other post-retirement benefits - Expected Benefit Payments (Detail)
$ in Thousands
Dec. 31, 2019
USD ($)
Pension Plans  
Defined Benefit Plan Disclosure [Line Items]  
2020 $ 34,461
2021 34,385
2022 35,383
2023 36,897
2024 37,848
2025-2029 192,648
Post Retirement Benefit Plan  
Defined Benefit Plan Disclosure [Line Items]  
2020 7,469
2021 7,867
2022 8,379
2023 8,903
2024 9,361
2025-2029 $ 52,864