Loans and Allowance for Credit Losses for Loans - Recorded Investment Based on Payment Activity - Non-PCI Loans (Details) - Non-PCI Loans $ in Thousands	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 6,527,016
Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	6,511,954
Non-Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	15,062
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	3,796,942
Residential mortgage | Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	3,784,084
Residential mortgage | Non-Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	12,858
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	376,020
Consumer | Home equity | Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	374,374
Consumer | Home equity | Non-Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	1,646
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	1,451,352
Consumer | Automobile | Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	1,451,018
Consumer | Automobile | Non-Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	334
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	902,702
Consumer | Other consumer | Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	902,478
Consumer | Other consumer | Non-Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 224