Pension Plans and Other Postretirement Benefits - Net Periodic Defined Benefit Cost for Defined Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,837	$ 4,423	$ 8,512	$ 13,237
Interest cost on projected benefit obligation	28,862	22,060	86,585	60,407
Expected return on plan assets	(50,315)	(50,188)	(150,945)	(137,421)
Amortization of prior service cost (credit)	52	129	155	387
Amortization of net actuarial loss (gain)	(537)	4,974	(1,610)	14,921
Net periodic cost (benefit)	$ (19,101)	$ (18,602)	$ (57,303)	$ (48,469)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 400	$ 689	$ 1,200	$ 1,914
Interest cost on projected benefit obligation	703	581	2,109	1,607
Amortization of prior service cost (credit)	(515)	(693)	(1,545)	(2,079)
Amortization of net actuarial loss (gain)	(692)	(370)	(2,076)	(1,111)
Net periodic cost (benefit)	$ (104)	$ 207	$ (312)	$ 331
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense