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Retirement Plans and Other Postretirement Benefits - Summary of Benefit Payments Expected to be Paid (Detail)
$ in Thousands
Dec. 31, 2017
USD ($)
Retirement Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 $ 2,745
2019 2,786
2020 2,829
2021 2,899
2022 2,901
Years 2023-2027 14,987
Other Post Retirement Benefits [Member]  
Defined Benefit Plan Disclosure [Line Items]  
2018 80
2019 85
2020 88
2021 91
2022 97
Years 2023-2027 $ 608