Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - Credit Quality Indicators by Class (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Loans	$ 14,653,188	$ 12,840,330
Commercial industrial and agricultural
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Loans	5,013,037	4,887,141
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]
Loans	4,635,571	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	377,466	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	4,903,300	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	1,950,406	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	868,293	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	631,607	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	1,452,994	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	11,112,875	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]
Loans		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]
Loans		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]
Loans		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]
Loans		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]
Loans	3,540,313	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]
Loans		3,258,232
Consumer 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]
Loans		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]
Loans	827,746	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]
Loans		843,011
Consumer loans | Home equity | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Loans		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]
Loans	2,287,555	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]
Loans		1,922,636
Consumer loans | 1-4 family mortgages | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Loans		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]
Loans	$ 425,012	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]
Loans		492,585
Consumer loans | Installment | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) [Line Items]
Loans		$ 0