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Employee benefit plans - Components of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Net periodic pension cost:        
Labor and Related Expense $ 8,037 $ 7,390 $ 15,632 $ 14,345
Pension Benefits        
Net periodic pension cost:        
Interest cost 192 156 320 156
Expected return on plan assets (325) (240) (542) (240)
Amortization of unrecognized net gain 68 49 113 49
Net periodic benefit cost $ (65) $ (35) $ (109) $ (35)