Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 9,243,833	$ 8,459,310
Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,875,331	2,109,879
Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	83,090	93,861
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	622,084	787,568
Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,248,506	3,052,698
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,146,406	1,143,217
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	527,458	588,984
Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	125,411	135,989
Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	615,547	547,114
Commercial Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,137,276	6,447,193
Commercial Pass | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,651,863	1,956,985
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	70,380	78,558
Commercial Pass | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	570,635	749,249
Commercial Pass | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,018,791	2,894,366
Commercial Pass | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	195,916	196,710
Commercial Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	14,218	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	615,473	547,114
Commercial Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	257,740	147,328
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	130,786	81,179
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,810	5,626
Commercial Special Mention | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,830	1,613
Commercial Special Mention | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	109,661	57,776
Commercial Special Mention | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,522	877
Commercial Special Mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	57	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	74	0
Commercial Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	240,931	190,358
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	92,682	71,715
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,900	9,677
Commercial Substandard | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	14,362	1,634
Commercial Substandard | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	118,721	98,575
Commercial Substandard | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,337	8,075
Commercial Substandard | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	929	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	1,601,238	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	26,135	35,072
Consumer Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,333	1,981
Consumer Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	938,731	932,743
Consumer Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	509,676	562,507
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	125,363	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	6,648	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	122	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	3,900	4,812
Consumer Non-Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,578	1,327
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	48	45
Consumer Non-Performing | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0