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Employee Benefit Plans - Estimated Future Benefit Payments for Defined Benefit Pension and Postretirement Benefit Plans (Detail)
$ in Thousands
Dec. 31, 2017
USD ($)
Postretirement benefit plans  
Defined Benefit Plan Disclosure [Line Items]  
2018 $ 60,433
2019 36,577
2020 36,500
2021 36,555
2022 37,686
2022 - 2026 182,421
Deferred compensation and excess benefit plans  
Defined Benefit Plan Disclosure [Line Items]  
2018 1,400
2019 1,200
2020 1,100
2021 1,100
2022 1,000
2022 - 2026 $ 2,600