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Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Obligation (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Weighted Average Assumptions Used to Determine Benefit Obligation    
First five years   1.96%
Five years to twenty years   3.58%
After twenty years   4.35%
Expected return on plan assets 1.00% 1.00%