Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Minimum pension liability	$ 155,000
Minimum pension liability adjustment net of tax	115,000
Decrease in minimum liability adjustment		$ 118,000
Defined contribution pension and retirement savings plans total expense	$ 56,000	45,000	$ 40,000
Assumptions used calculating net periodic benefit sensitivity rate increase decrease discount rate	25.00%
Effect of 25 basis point increase in rate of return on pension expense	$ 8,000
Effect of 25 basis point decrease in rate of return on pension expense	1,000
Effect of 25 basis point decrease in discount rate on benefit obligation	62,000
Effect of 25 basis point increase in discount rate on benefit obligation	$ 65,000
Annual rate of increase in health care cost assumed for next fiscal year	6.75%
Defined Benefit Plan, ultimate health care cost trend rate	5.00%
Period for decreasing the annual rate	over seven years
Defined benefit pension plans	$ 668,000
Percentage of total assets	21.00%
Defined benefit plan fair value of plan assets	$ 3,141,000	2,938,000
Qualified benefit pension plans	$ 0
Percentage of pension plan assets that is not exceeded by investment in security of single Non-US Government of Government agency	10.00%
Percentage of eligible employees contribution for Retirement Savings Plan	50.00%
Percentage of employer matching contribution to employee's contribution	100.00%
Maximum employer contribution on Employee's qualified contribution	5.00%
Qualified defined contribution plans expense during the period	$ 96,000	$ 84,000	63,000
Increment in amortization period		16 years
Defined benefit pension plan, reduction to change in amortization		$ 36,000
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Immediate Recognition of Actuarial Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Other Noninterest Expense
Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	5.00%
Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	60.00%
Total Debt Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	10.00%
Total Debt Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	65.00%
Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 668,000	$ 632,000
Other Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	5.00%
Other Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	60.00%
M&T Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 112,000	118,000
Supplemental Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	146,000	152,000
Accumulated benefit obligation	146,000	152,000
Employer contribution	18,000	14,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	2,369,000	2,379,000	2,420,000
Accumulated benefit obligation	2,400,000	$ 2,400,000
Minimum pension liability	$ 191,000
Discount rate	5.00%	5.00%
Defined benefit plan fair value of plan assets	$ 3,145,000	$ 2,942,000	2,596,000
Employer contribution	18,000	14,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	57,000	$ 60,000	$ 52,000
Minimum pension liability	$ 36,000
Discount rate	5.00%	5.00%
Employer contribution	$ 3,000	$ 3,000