Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 7,299,320	$ 7,224,467
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,788,628	1,726,664
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	80,357	92,404
Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	542,501	545,729
Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,838,798	2,832,102
Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	976,668	966,421
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	536,208	528,157
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	108,216	99,788
Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	427,944	433,202
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,524,130	5,528,751
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,692,964	1,660,879
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	64,022	78,446
Commercial Pass | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	507,086	492,358
Commercial Pass | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,640,736	2,669,491
Commercial Pass | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	167,197	170,075
Commercial Pass | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	24,534	24,653
Commercial Pass | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Pass | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	427,591	432,849
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	167,961	115,342
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	59,119	23,246
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	6,304	5,966
Commercial Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	949	2,185
Commercial Special Mention | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	96,353	76,037
Commercial Special Mention | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,747	7,373
Commercial Special Mention | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	489	535
Commercial Special Mention | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Special Mention | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	158,749	161,929
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	36,545	42,539
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	10,031	7,992
Commercial Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	9,063	24,224
Commercial Substandard | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	99,363	84,288
Commercial Substandard | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	2,992	2,076
Commercial Substandard | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	402	457
Commercial Substandard | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Substandard | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	353	353
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Doubtful | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Loss | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,442,324	1,410,521
Consumer Performing | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	25,403	25,419
Consumer Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,346	2,285
Consumer Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	797,420	782,080
Consumer Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	508,969	500,996
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	108,186	99,741
Consumer Performing | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	6,156	7,924
Consumer Non-Performing | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer Non-Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer Non-Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,543
Consumer Non-Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1
Consumer Non-Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,312	4,817
Consumer Non-Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,814	1,516
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	30	47
Consumer Non-Performing | Public finance and other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0