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Retirement Plans and Other Post-Retirement Benefits - Summary of Benefit Expected to be Paid Out (Detail)
$ in Thousands
Dec. 31, 2017
USD ($)
Pension Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 $ 41,106
2019 39,993
2020 39,468
2021 39,375
2022 39,041
2023 through 2027 188,907
Other Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 3,500
2019 4,129
2020 4,500
2021 4,663
2022 4,620
2023 through 2027 $ 21,053