Pension and Postretirement Benefits - Schedule of Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7,711	$ 7,911	$ 23,133	$ 23,732
Interest cost	9,424	8,307	28,280	24,921
Expected return on assets	(11,929)	(11,516)	(35,864)	(34,549)
Prior service cost (credit)	2	27	5	77
Actuarial loss (gain)	3,927	3,206	11,852	9,621
Settlement charge		2,692		2,692
Net periodic benefit cost (credit)	9,135	10,627	27,406	26,494
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	15	19	44	58
Interest cost	131	130	437	389
Prior service cost (credit)	(190)	(519)	(571)	(1,556)
Actuarial loss (gain)	(114)	(53)	(387)	(158)
Net periodic benefit cost (credit)	$ (158)	$ (423)	$ (477)	$ (1,267)