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Employee Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Defined benefit pension plans        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 1,198 $ 1,609 $ 3,441 $ 4,293
Interest cost 4,479 6,107 13,370 18,407
Expected return on plan assets (5,768) (6,393) (17,253) (19,309)
Amortization of prior service cost 8 8 23 23
Recognized actuarial loss 1,823 1,732 5,464 5,194
Settlement loss 0 1,495 0 1,495
Net periodic benefit cost 1,740 4,558 5,045 10,103
Postretirement benefit plans        
Defined Benefit Plan Disclosure [Line Items]        
Service cost 0 13 1 39
Interest cost 203 286 609 857
Recognized actuarial loss 37 37 112 111
Net periodic benefit cost $ 240 $ 336 $ 722 $ 1,007