Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,709,907	$ 4,693,822
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,060,559	1,057,075
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	92,137	97,711
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	391,621	366,704
Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,806,395	1,802,921
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	769,592	786,105
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	353,946	348,613
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	73,622	74,717
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	461	588
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	161,574	159,388
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,395,816	3,404,491
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	984,052	962,340
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	48,604	77,884
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	365,808	345,449
Commercial Pass | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,669,322	1,679,141
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	158,931	171,576
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	7,164	8,218
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	371	495
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	161,564	159,388
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	137,315	105,965
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	46,952	48,432
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	22,829	6,665
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	4,021	1,271
Commercial Special Mention | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	55,336	46,442
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	8,095	3,107
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	72	48
Commercial Special Mention | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	10
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	146,801	149,395
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	29,555	45,984
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	20,704	13,162
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	3,441	1,790
Commercial Substandard | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	81,737	77,338
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	10,706	10,428
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	568	600
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 90	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	$ 1,019,668	$ 1,023,856
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	18,272	18,114
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	584,262	593,533
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	343,812	337,718
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	73,322	74,491
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	10,307	9,796
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 79	$ 80
Consumer Non-Performing | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans
Consumer Non-Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 7,598	$ 7,461
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	2,330	2,029
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 300	$ 226