Loans and Allowance - Composition of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 9,041,576	$ 9,243,174
Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,573,615	2,776,699
Agricultural land, production and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	240,686	281,884
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	521,889	484,723
Commercial real estate, non-owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,150,387	2,220,949
Commercial real estate, owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	952,441	958,501
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,154,373	1,234,741
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	531,307	508,259
Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	135,093	129,479
Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 781,785	$ 647,939