Allowance for Credit Losses - Credit Risk Profiles Based on Payment Activity, Not Subject to Loan Grading (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	$ 13,499,969	$ 13,211,650
Consumer loans
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		226,304
Consumer loans | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		219,046
Consumer loans | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		7,258
Residential and consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		6,282,731
Residential and consumer | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		6,229,130
Residential and consumer | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		53,601
Residential
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		4,662,175
Residential | Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	3,669,051	3,768,936
Home equity Line | Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	864,789	893,239
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		1,620,556
Consumer | Consumer loans
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	$ 1,425,934	1,620,556
Consumer | Consumer - Auto
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		1,040,468
Consumer | Consumer - Auto | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		1,016,142
Consumer | Consumer - Auto | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		24,326
Consumer | Credit Cards
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		353,784
Consumer | Credit Cards | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		347,264
Consumer | Credit Cards | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		6,520
Residential Mortgage.
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		3,768,936
Residential Mortgage. | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		3,759,799
Residential Mortgage. | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		9,137
Home equity line
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		893,239
Home equity line | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		886,879
Home equity line | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		$ 6,360