Pension Plans and Other Postretirement Benefits - Data Relating to Funding Position of Defined Benefit Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Change in plan assets:
Fair value of plan assets at beginning of year	$ 2,593,533
Fair value of plan assets at end of year	2,938,404	$ 2,593,533
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	2,420,213	2,521,292
Service cost	17,660	20,513	$ 19,944
Interest cost	$ 82,467	$ 61,873	$ 71,421
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
Actuarial (gain) loss	$ (636,220)	$ (69,230)
Business combinations	632,855
Benefits paid	(137,987)	(114,235)
Benefit obligation at end of year	2,378,988	2,420,213	$ 2,521,292
Change in plan assets:
Fair value of plan assets at beginning of year	2,595,838	2,420,582
Actual return on plan assets	(385,823)	278,260
Employer contributions	14,397	11,231
Business combinations	855,555
Benefits paid	(137,987)	(114,235)
Fair value of plan assets at end of year	2,941,980	2,595,838	2,420,582
Funded status	562,992	(175,625)
Prepaid asset recognized in the consolidated balance sheet	715,418	332,197
Accrued liability recognized in the consolidated balance sheet	(152,426)	(156,572)
Net accrued asset (liability) recognized in the consolidated balance sheet	562,992	(175,625)
Net loss (gain)	309,039	391,721
Net prior service cost (credit)	208	724
Pre-tax adjustment to AOCI	309,247	392,445
Taxes	(80,095)	(101,447)
Net adjustment to AOCI	229,152	290,998
Other Postretirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	51,846	55,281
Service cost	2,604	1,014	970
Interest cost	$ 2,188	$ 1,311	$ 1,741
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
Plan participants’ contributions	$ 2,433	$ 2,553
Actuarial (gain) loss	(21,735)	(2,232)
Plan amendment	13,260
Business combinations	14,859
Medicare Part D reimbursement	506	540
Benefits paid	(5,600)	(6,621)
Benefit obligation at end of year	60,361	51,846	$ 55,281
Change in plan assets:
Employer contributions	2,661	3,528
Plan participants’ contributions	2,433	2,553
Medicare Part D reimbursement	506	540
Benefits paid	(5,600)	(6,621)
Funded status	(60,361)	(51,846)
Accrued liability recognized in the consolidated balance sheet	(60,361)	(51,846)
Net accrued asset (liability) recognized in the consolidated balance sheet	(60,361)	(51,846)
Net loss (gain)	(34,892)	(14,638)
Net prior service cost (credit)	(1,499)	(17,531)
Pre-tax adjustment to AOCI	(36,391)	(32,169)
Taxes	9,425	8,316
Net adjustment to AOCI	$ (26,966)	$ (23,853)