Loans and Allowance for Credit Losses for Loans - Recorded Investment in Loan Classes Based on Payment Activity (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 6,527,016
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,629,599
Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,511,954
Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,559,439
Non-Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	15,062
Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	70,160
Residential mortgage | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,796,942
Residential mortgage | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	580,169
Residential mortgage | Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,784,084
Residential mortgage | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	571,006
Residential mortgage | Non-Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	12,858
Residential mortgage | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	9,163
Consumer | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	122,267
Consumer | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	120,356
Consumer | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,911
Consumer | Home equity | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	376,020
Consumer | Home equity | Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	374,374
Consumer | Home equity | Non-Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,646
Consumer | Automobile Loan | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,451,352
Consumer | Automobile Loan | Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,451,018
Consumer | Automobile Loan | Non-Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	334
Consumer | Other consumer | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	902,702
Consumer | Other consumer | Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	902,478
Consumer | Other consumer | Non-Performing Loans | Non Purchased Credit Impaired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	224
Commercial and industrial | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	682,014
Commercial and industrial | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	653,997
Commercial and industrial | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	28,017
Commercial real estate | Commercial real estate | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	5,093,848
Commercial real estate | Commercial real estate | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	5,065,388
Commercial real estate | Commercial real estate | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	28,460
Commercial real estate | Construction | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	151,301
Commercial real estate | Construction | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	148,692
Commercial real estate | Construction | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 2,609