Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,238,205	$ 3,924,865
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	984,223	896,688
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	93,695	104,927
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	256,082	207,221
Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,705,647	1,672,661
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	689,621	647,315
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	302,403	286,529
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	62,785	73,400
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	742	1,106
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	143,007	35,018
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,147,595	2,849,876
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	913,859	823,732
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	84,781	96,155
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	237,568	185,394
Commercial Pass | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,586,935	1,552,781
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	173,714	149,430
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	7,088	6,368
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	643	998
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	143,007	35,018
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	75,452	64,631
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	24,180	24,455
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	3,002	1,195
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,611	3,164
Commercial Special Mention | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	43,895	29,484
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	2,698	6,321
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 66	12
Commercial Special Mention | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 141,167	160,608
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	46,184	48,226
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	5,912	7,577
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,268	2,928
Commercial Substandard | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	74,815	90,161
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	12,417	10,918
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	472	690
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 99	$ 108
Commercial Substandard | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 565	$ 275
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 275
Commercial Doubtful | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 565
Commercial Doubtful | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 866,382	$ 837,296
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	14,967	15,588
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	495,678	470,972
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	293,071	277,571
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	62,666	73,165
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	7,044	12,179
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	103	147
Consumer Non-Performing | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2	235
Consumer Non-Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	5,114	9,674
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,706	1,888
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 119	$ 235