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Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 101 $ 112 $ 315 $ 335
Interest cost 329 356 986 1,069
Expected return on plan assets (431) (457) (1,292) (1,371)
Amortization of net actuarial loss 57 53 170 159
Net periodic benefit cost 56 64 179 192
Health Care Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 1 1 2 3
Amortization of loss 2 3 6 8
Net periodic benefit cost $ 3 $ 4 $ 8 $ 11