Allowance for Credit Losses - Credit Risk Profiles Based on Payment Activity, Not Subject to Loan Grading (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	$ 13,380,270	$ 13,211,650
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	3,673,455	3,768,936
Home equity Line | Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	891,698	893,239
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	1,568,073	1,620,556
Consumer | Consumer loans
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases	$ 1,568,073	1,620,556
Not subject to loan grading | Residential and consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		6,282,731
Not subject to loan grading | Residential and consumer | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		6,229,130
Not subject to loan grading | Residential and consumer | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		53,601
Not subject to loan grading | Residential | Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		3,768,936
Not subject to loan grading | Residential | Residential mortgage | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		3,759,799
Not subject to loan grading | Residential | Residential mortgage | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		9,137
Not subject to loan grading | Home equity Line | Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		893,239
Not subject to loan grading | Home equity Line | Home equity | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		886,879
Not subject to loan grading | Home equity Line | Home equity | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		6,360
Not subject to loan grading | Consumer | Consumer - Auto
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		1,040,468
Not subject to loan grading | Consumer | Consumer - Auto | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		1,016,142
Not subject to loan grading | Consumer | Consumer - Auto | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		24,326
Not subject to loan grading | Consumer | Credit Cards
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		353,784
Not subject to loan grading | Consumer | Credit Cards | Performing
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		347,264
Not subject to loan grading | Consumer | Credit Cards | Non-performing and delinquent
Loans and Leases Receivable Disclosure [Line Items]
Loans and leases		$ 6,520