Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 7,511,370	$ 7,224,467
Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,877,042	1,726,664
Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	83,452	92,404
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	624,548	545,729
Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,821,689	2,832,102
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	993,802	966,421
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	548,006	528,157
Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	98,384	99,788
Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	464,447	433,202
Commercial Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,734,217	5,528,751
Commercial Pass | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,781,040	1,660,879
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	67,837	78,446
Commercial Pass | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	591,962	492,358
Commercial Pass | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,645,338	2,669,491
Commercial Pass | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	156,622	170,075
Commercial Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	27,324	24,653
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	464,094	432,849
Commercial Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	146,333	115,342
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	53,407	23,246
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,478	5,966
Commercial Special Mention | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,444	2,185
Commercial Special Mention | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	79,586	76,037
Commercial Special Mention | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,833	7,373
Commercial Special Mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	585	535
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	0	0
Commercial Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	158,830	161,929
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	42,266	42,539
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,137	7,992
Commercial Substandard | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,712	24,224
Commercial Substandard | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	94,179	84,288
Commercial Substandard | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,425	2,076
Commercial Substandard | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	758	457
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	353	353
Commercial Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	779	0
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	329	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	450	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	1,464,815	1,410,521
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	23,430	25,419
Consumer Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,136	2,285
Consumer Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	823,309	782,080
Consumer Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	517,620	500,996
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	98,320	99,741
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	6,396	7,924
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		1,543
Consumer Non-Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	1
Consumer Non-Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,613	4,817
Consumer Non-Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,719	1,516
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	64	47
Consumer Non-Performing | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0