Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 8,606,849	$ 8,459,310
Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,199,226	2,109,879
Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	87,421	93,861
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	643,674	787,568
Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,268,168	3,052,698
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,121,556	1,143,217
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	570,398	588,984
Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	129,765	135,989
Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	586,641	547,114
Commercial Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,618,263	6,447,193
Commercial Pass | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,024,943	1,956,985
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	70,365	78,558
Commercial Pass | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	591,599	749,249
Commercial Pass | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,120,084	2,894,366
Commercial Pass | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	200,792	196,710
Commercial Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	24,273	24,211
Commercial Pass | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Pass | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	586,207	547,114
Commercial Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	170,639	147,328
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	93,686	81,179
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,962	5,626
Commercial Special Mention | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	20,043	1,613
Commercial Special Mention | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	49,714	57,776
Commercial Special Mention | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	395	877
Commercial Special Mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	405	257
Commercial Special Mention | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Special Mention | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	434	0
Commercial Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	196,841	190,358
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	80,597	71,715
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	11,094	9,677
Commercial Substandard | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,466	1,634
Commercial Substandard | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	96,451	98,575
Commercial Substandard | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,439	8,075
Commercial Substandard | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	794	682
Commercial Substandard | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Substandard | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,615,465	1,668,247
Consumer Performing | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Performing | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	30,449	35,072
Consumer Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,919	1,981
Consumer Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	909,813	932,743
Consumer Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	543,579	562,507
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	129,705	135,944
Consumer Performing | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,641	6,184
Consumer Non-Performing | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	117	0
Consumer Non-Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,117	4,812
Consumer Non-Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,347	1,327
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	60	45
Consumer Non-Performing | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0