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Components of Net Periodic Benefit Cost of Health and Welfare Plan (Detail) - Post-Retirement Benefits - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Components of Net Periodic Benefit Cost:      
Service cost     $ 5
Interest cost $ 513 $ 577 639
Amortization of past-service liability (249) (249) (249)
Amortization of net actuarial loss 309 274 326
Net periodic benefit cost $ 573 $ 602 $ 721