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Stock-based Compensation Plans - Additional Information 5 (Detail) - Other Post Retirement Benefit Plan
Dec. 31, 2018
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Expected future benefit payments for the five year period 2019 through 2023 $ 497,000
Expected future benefit payments for the five year period 2024 through 2028 534,000
Estimated prior service cost amortized from accumulated other comprehensive (loss) income into statement of operation in 2019 $ 369,000