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Benefit Plans - Net Periodic Benefit Cost (Increase) (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 0 $ 0 $ 0
Interest cost 1,000 1,198 1,094
Return on plan assets (2,949) (2,562) (2,769)
Amortization of net loss (gain) 696 1,015 795
Amortization of unrecognized prior service cost 0 0 0
Net periodic (benefit) increase cost (1,253) (349) (880)
Post-retirement      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 78 80 115
Interest cost 712 837 786
Return on plan assets 0 0 0
Amortization of net loss (gain) (248) (825) (396)
Amortization of unrecognized prior service cost 0 0 0
Net periodic (benefit) increase cost $ 542 $ 92 $ 505