Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,791,429	$ 4,693,822
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,084,890	1,057,075
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	95,131	97,711
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	352,980	366,704
Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,869,703	1,802,921
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	758,870	786,105
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	374,159	348,613
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	75,205	74,717
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	388	588
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	180,103	159,388
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,466,456	3,404,491
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,022,507	962,340
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	37,114	77,884
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	328,366	345,449
Commercial Pass | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,733,503	1,679,141
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	157,186	171,576
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	7,377	8,218
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	300	495
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	180,103	159,388
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	126,767	105,965
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	29,117	48,432
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	32,784	6,665
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	5,023	1,271
Commercial Special Mention | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	51,793	46,442
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	7,953	3,107
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	97	48
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	151,695	149,395
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	33,266	45,984
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	25,233	13,162
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,606	1,790
Commercial Substandard | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	84,407	77,338
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	6,352	10,428
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	743	600
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	88	93
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans		319
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans		319
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,036,013	1,023,856
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	17,908	18,114
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	579,403	593,533
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	363,618	337,718
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	75,084	74,491
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	10,498	9,796
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	77	80
Consumer Non-Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	7,976	7,461
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	2,324	2,029
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 121	$ 226