Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,321,715	$ 3,924,865
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	999,195	896,688
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	91,354	104,927
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	298,250	207,221
Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,695,703	1,672,661
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	677,767	647,315
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	318,949	286,529
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	71,893	73,400
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	614	1,106
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	167,990	35,018
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,214,297	2,849,876
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	927,042	823,732
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	73,793	96,155
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	280,673	185,394
Commercial Pass | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,588,797	1,552,781
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	168,287	149,430
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	7,195	6,368
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	520	998
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	167,990	35,018
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	79,060	64,631
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	30,679	24,455
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	4,750	1,195
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,151	3,164
Commercial Special Mention | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	40,199	29,484
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	2,265	6,321
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	16	12
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	134,093	160,608
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	41,444	48,226
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	12,811	7,577
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,230	2,928
Commercial Substandard | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	66,705	90,161
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	11,325	10,918
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	484	690
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	94	108
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans		275
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans		275
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans	30
Commercial Loss | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	30
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	886,865	837,296
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	15,114	15,588
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	490,657	470,972
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	309,403	277,571
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	71,691	73,165
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	7,370	12,179
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	82	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	5,233	9,674
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,851	1,888
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 202	$ 235