Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Current	$ 9,212,238	$ 9,170,399
Loans	9,318,228	9,243,174
Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Current	2,870,436	2,761,473
Loans	2,876,212	2,776,699
Agricultural land, production and other loans to farmers
Financing Receivable, Past Due [Line Items]
Current	244,403	280,615
Loans	245,631	281,884
Construction
Financing Receivable, Past Due [Line Items]
Current	540,648	484,706
Loans	541,224	484,723
Commercial real estate, non-owner occupied
Financing Receivable, Past Due [Line Items]
Current	2,094,103	2,184,681
Loans	2,178,832	2,220,949
Commercial real estate, owner occupied
Financing Receivable, Past Due [Line Items]
Current	946,423	951,561
Loans	950,038	958,501
Residential Real Estate
Financing Receivable, Past Due [Line Items]
Current	1,234,473	1,226,779
Loans	1,239,925	1,234,741
Home equity
Financing Receivable, Past Due [Line Items]
Current	477,927	503,596
Loans	482,229	508,259
Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Current	126,075	129,049
Loans	126,387	129,479
Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Current	677,750	647,939
Loans	677,750	647,939
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	55,622	19,638
30-59 Days Past Due \| Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Past Due	4,545	5,866
30-59 Days Past Due \| Agricultural land, production and other loans to farmers
Financing Receivable, Past Due [Line Items]
Past Due	114	146
30-59 Days Past Due \| Construction
Financing Receivable, Past Due [Line Items]
Past Due	560	0
30-59 Days Past Due \| Commercial real estate, non-owner occupied
Financing Receivable, Past Due [Line Items]
Past Due	45,942	2,525
30-59 Days Past Due \| Commercial real estate, owner occupied
Financing Receivable, Past Due [Line Items]
Past Due	792	4,854
30-59 Days Past Due \| Residential Real Estate
Financing Receivable, Past Due [Line Items]
Past Due	1,582	3,269
30-59 Days Past Due \| Home equity
Financing Receivable, Past Due [Line Items]
Past Due	1,906	2,644
30-59 Days Past Due \| Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Past Due	181	334
30-59 Days Past Due \| Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	2,978	11,187
60-89 Days Past Due \| Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Past Due	19	6,571
60-89 Days Past Due \| Agricultural land, production and other loans to farmers
Financing Receivable, Past Due [Line Items]
Past Due	0	226
60-89 Days Past Due \| Construction
Financing Receivable, Past Due [Line Items]
Past Due	0	17
60-89 Days Past Due \| Commercial real estate, non-owner occupied
Financing Receivable, Past Due [Line Items]
Past Due	434	2,109
60-89 Days Past Due \| Commercial real estate, owner occupied
Financing Receivable, Past Due [Line Items]
Past Due	1,096	180
60-89 Days Past Due \| Residential Real Estate
Financing Receivable, Past Due [Line Items]
Past Due	377	1,429
60-89 Days Past Due \| Home equity
Financing Receivable, Past Due [Line Items]
Past Due	1,010	559
60-89 Days Past Due \| Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Past Due	42	96
60-89 Days Past Due \| Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due	47,390	41,950
Loans > 90 Days or More Past Due And Accruing	1,093	746
90 Days or More Past Due \| Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Past Due	1,212	2,789
Loans > 90 Days or More Past Due And Accruing	0	594
90 Days or More Past Due \| Agricultural land, production and other loans to farmers
Financing Receivable, Past Due [Line Items]
Past Due	1,114	897
Loans > 90 Days or More Past Due And Accruing	0	0
90 Days or More Past Due \| Construction
Financing Receivable, Past Due [Line Items]
Past Due	16	0
Loans > 90 Days or More Past Due And Accruing	0	0
90 Days or More Past Due \| Commercial real estate, non-owner occupied
Financing Receivable, Past Due [Line Items]
Past Due	38,353	31,634
Loans > 90 Days or More Past Due And Accruing	0	0
90 Days or More Past Due \| Commercial real estate, owner occupied
Financing Receivable, Past Due [Line Items]
Past Due	1,727	1,906
Loans > 90 Days or More Past Due And Accruing	1,032	0
90 Days or More Past Due \| Residential Real Estate
Financing Receivable, Past Due [Line Items]
Past Due	3,493	3,264
Loans > 90 Days or More Past Due And Accruing	0	133
90 Days or More Past Due \| Home equity
Financing Receivable, Past Due [Line Items]
Past Due	1,386	1,460
Loans > 90 Days or More Past Due And Accruing	60	19
90 Days or More Past Due \| Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Past Due	89	0
Loans > 90 Days or More Past Due And Accruing	1	0
90 Days or More Past Due \| Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Loans > 90 Days or More Past Due And Accruing	$ 0	$ 0