Summary of Significant Accounting Policies - Additional Information (Details)		12 Months Ended
	Jan. 01, 2020 USD ($)	Dec. 31, 2020 USD ($) segment plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Unfunded commitments to fund low-income housing partnerships		$ 52,959,000
Variable interest entity, nonconsolidated, carrying amount, assets		20,603,651,000	$ 18,095,496,000	$ 17,143,974,000
Trading securities		$ 0	0
Number of portfolio segments of loans and leases (commercial and consumer) | segment		2
Period during which non-accrual loan that has been modified in a troubled debt restructuring remains on non-accrual status (in months)		6 months
Allowance for accrued interest receivable		$ 2,700,000
CARES Act estimated provision for relief measures		$ 2,200,000,000,000
Maximum original maturity period of cash and cash equivalents (in days)		90 days
Goodwill impairment		$ 0
Number of company's pension plans | plan		2
Minimum percentage of net actuarial gain (loss) will be amortized in net periodic benefit cost		10.00%
Minimum percentage of likelihood of tax position being realized upon ultimate settlement according to management's judgment		50.00%
Advertising costs		$ 8,300,000	6,100,000	$ 6,000,000.0
Accounting Standards Update 2016-13
Summary Of Significant Accounting Policies [Line Items]
Total reserve for credit losses			116,849,000
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Total reserve for credit losses	$ (5,072,000)
Increase to retained earnings	$ 3,632,000
ASU No. 2018-13
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Dec. 15, 2019
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
Change in Accounting Principle, Accounting Standards Update, Early Adoption [true false]		true
ASU No. 2019-04
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Dec. 15, 2019
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
ASU No. 2019-05
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
ASU No. 2019-11
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
Maximum | Building
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives (in years)		30 years
Maximum | Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives (in years)		10 years
Home Equity
Summary Of Significant Accounting Policies [Line Items]
Minimum maturity period to be considered to place loans and leases on non-accrual status (in days)		120 days
Home Equity | Maximum
Summary Of Significant Accounting Policies [Line Items]
Combined loan-to-value ratio, considered in determining whether the entire outstanding balance on the loan is to be charged-off or not (as a percent)		60.00%
Commercial
Summary Of Significant Accounting Policies [Line Items]
Minimum maturity period to be considered to place loans and leases on non-accrual status (in days)		90 days
Residential Mortgage and Home Equity Loan
Summary Of Significant Accounting Policies [Line Items]
Minimum maturity period to be considered to place loans and leases on non-accrual status (in days)		120 days
Automobile and Other consumer
Summary Of Significant Accounting Policies [Line Items]
Minimum maturity period to be considered for loans and leases to be charged off (in days)		120 days
Commercial and Industrial
Summary Of Significant Accounting Policies [Line Items]
Minimum maturity period to be considered for loans and leases to be charged off (in days)		120 days
Other Liabilities
Summary Of Significant Accounting Policies [Line Items]
Unfunded commitments to fund low-income housing partnerships		$ 53,000,000.0	21,300,000
Low-income Housing Partnerships
Summary Of Significant Accounting Policies [Line Items]
Period over which Federal tax credits or benefits are generally recognized (in years)		10 years
Period over which State tax credits or benefits are generally recognized (in years)		5 years
Solar Energy Partnerships
Summary Of Significant Accounting Policies [Line Items]
Period over which Federal tax credits or benefits are generally recognized (in years)		6 years
Variable Interest Entity Nonconsolidated | Other Assets
Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, nonconsolidated, carrying amount, assets		$ 143,000,000.0	$ 84,600,000