Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Minimum pension liability	$ 449,916,000
Minimum pension liability adjustment net of tax	272,874,000
Decrease in minimum liability adjustment		$ 39,743,000
Increase in minimum pension liability adjustment net of tax		24,105,000
Defined contribution pension and retirement savings plans total expense	$ 25,000,000	23,000,000	$ 22,000,000
Annual rate of increase in health care cost assumed for next fiscal year	6.50%
Defined Benefit Plan, ultimate health care cost trend rate	5.00%
Period for decreasing the annual rate	Over 12 years
Defined benefit pension plans	$ 234,969,000
Percentage of total assets	14.30%
Defined benefit plan fair value of plan assets	$ 1,640,300,000	1,623,635,000
Qualified benefit pension plans	$ 0	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	75.00%
Maximum employer contribution on Employee's qualified contribution	4.50%
Qualified defined contribution plans expense during the period	$ 36,766,000	34,145,000	32,466,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, minimum range	25.00%
Target allocations for plan assets, maximum range	60.00%
Defined benefit plan fair value of plan assets	$ 920,077,000	1,059,758,000
Total Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, minimum range	10.00%
Target allocations for plan assets, maximum range	65.00%
Defined benefit plan fair value of plan assets	$ 445,698,000	284,365,000
Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, minimum range	10.00%
Target allocations for plan assets, maximum range	85.00%
Defined benefit plan fair value of plan assets	$ 234,969,000	209,878,000
M&T Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 164,474,000	$ 148,800,000
Percentage of common stock in total plan assets	10.00%	9.20%
Supplemental Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 160,433,000
Accumulated benefit obligation		$ 161,657,000
Employer contributions	10,772,000	8,367,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	2,007,158,000	2,004,531,000	1,813,409,000
Accumulated benefit obligation	1,979,225,000	1,951,425,000
Minimum pension liability	464,066,000
Defined benefit plan fair value of plan assets	1,642,131,000	1,625,134,000	1,505,661,000
Employer contributions	10,772,000	8,367,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	109,922,000	121,497,000	$ 67,502,000
Minimum pension liability	14,150,000
Employer contributions	$ 7,588,000	$ 4,022,000