Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - Credit Quality Indicators by Class (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Commercial Industrial And Agricultural | Commercial and industrial
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		$ 4,481,525
Commercial Industrial And Agricultural | Commercial and industrial | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		4,324,709
Commercial Industrial And Agricultural | Commercial and industrial | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		47,665
Commercial Industrial And Agricultural | Commercial and industrial | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		79,156
Commercial Industrial And Agricultural | Commercial and industrial | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		29,995
Commercial Industrial And Agricultural | Agricultural
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		405,616
Commercial Industrial And Agricultural | Agricultural | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		350,827
Commercial Industrial And Agricultural | Agricultural | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		32,764
Commercial Industrial And Agricultural | Agricultural | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		16,071
Commercial Industrial And Agricultural | Agricultural | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		5,954
Commercial Real Estate
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		4,682,072
Commercial Real Estate | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		4,446,552
Commercial Real Estate | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		108,274
Commercial Real Estate | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		93,811
Commercial Real Estate | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		33,435
Commercial Real Estate | Office, retail, and industrial
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		1,848,718
Commercial Real Estate | Office, retail, and industrial | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		1,747,287
Commercial Real Estate | Office, retail, and industrial | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		42,230
Commercial Real Estate | Office, retail, and industrial | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		33,344
Commercial Real Estate | Office, retail, and industrial | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		25,857
Commercial Real Estate | Multi-family
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		856,553
Commercial Real Estate | Multi-family | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		839,615
Commercial Real Estate | Multi-family | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		8,279
Commercial Real Estate | Multi-family | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		5,962
Commercial Real Estate | Multi-family | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		2,697
Commercial Real Estate | Construction
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		593,093
Commercial Real Estate | Construction | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		564,495
Commercial Real Estate | Construction | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		17,977
Commercial Real Estate | Construction | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		10,469
Commercial Real Estate | Construction | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		152
Commercial Real Estate | Other commercial real estate
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		1,383,708
Commercial Real Estate | Other commercial real estate | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		1,295,155
Commercial Real Estate | Other commercial real estate | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		39,788
Commercial Real Estate | Other commercial real estate | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		44,036
Commercial Real Estate | Other commercial real estate | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		4,729
Total corporate loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		9,569,213
Total corporate loans | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		9,122,088
Total corporate loans | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		188,703
Total corporate loans | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		189,038
Total corporate loans | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		69,384
Consumer loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		3,271,117
Consumer loans | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		3,258,232
Consumer loans | Nonperforming
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		12,885
Consumer loans | Home equity
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable	$ 965,771	851,454
Consumer loans | Home equity | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		843,011
Consumer loans | Home equity | Nonperforming
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		8,443
Consumer loans | 1-4 family mortgages
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		1,927,078
Consumer loans | 1-4 family mortgages | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		1,922,636
Consumer loans | 1-4 family mortgages | Nonperforming
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		4,442
Consumer loans | Installment
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable	$ 488,515	492,585
Consumer loans | Installment | Performing
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		492,585
Consumer loans | Installment | Nonperforming
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Financing receivable		$ 0