Pension Plans and Other Postretirement Benefits - Net Periodic Defined Benefit Cost for Defined Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,952	$ 4,543	$ 5,675	$ 8,814
Interest cost on projected benefit obligation	28,888	22,080	57,723	38,347
Expected return on plan assets	(50,230)	(50,083)	(100,630)	(87,233)
Amortization of prior service cost (credit)	53	133	103	258
Amortization of net actuarial loss (gain)	(173)	5,322	(1,073)	9,947
Net periodic cost (benefit)	$ (18,510)	$ (18,005)	$ (38,202)	$ (29,867)
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	$ 410	$ 993	$ 800	$ 1,225
Interest cost on projected benefit obligation	662	671	1,406	1,026
Amortization of prior service cost (credit)	(505)	(311)	(1,030)	(1,386)
Amortization of net actuarial loss (gain)	(734)	(416)	(1,384)	(741)
Net periodic cost (benefit)	$ (167)	$ 937	$ (208)	$ 124
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