Accumulated Other Comprehensive Loss, net - Components of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Net Unrealized Gains (Losses) on Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in net unrealized holding gains on securities, before reclassification, tax benefit	$ 203	$ 30
Reclassification for previously unrealized net gains recognized in income, tax expense		0
Pension and Post-retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net gain pension and postretirement plans, tax expense	$ 157	$ 41

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) before reclassification adjustment from accumulated other comprehensive income (loss).

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