Loans and Allowance - Composition of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 9,121,250	$ 9,243,174
Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,671,076	2,776,699
Agricultural land, production and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	235,020	281,884
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	491,200	484,723
Commercial real estate, non-owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,263,497	2,220,949
Commercial real estate, owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	953,501	958,501
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,127,442	1,234,741
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	489,997	508,259
Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	130,819	129,479
Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 758,698	$ 647,939