Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 5,274,909	$ 5,139,645
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,258,840	1,194,646
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	77,021	79,689
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	336,931	418,703
Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,118,431	1,953,062
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	737,918	739,169
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	423,708	418,525
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	77,590	77,479
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	261	311
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	244,209	258,061
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,899,025	3,769,920
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,190,546	1,117,545
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	23,236	30,712
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	319,724	398,646
Commercial Pass | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,963,654	1,811,367
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	148,677	146,251
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	9,588	7,310
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	261	228
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	243,339	257,861
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	134,800	124,863
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	25,537	30,919
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	34,044	25,273
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	5,138	3,490
Commercial Special Mention | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	65,537	60,028
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,497	5,106
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	47	47
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	156,654	159,215
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	42,757	46,182
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	19,741	23,704
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	58	1,858
Commercial Substandard | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	87,197	80,626
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	5,679	6,046
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	352	516
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans		83
Commercial Substandard | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	870	200
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	1,687
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans
Commercial Doubtful | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,687
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,073,584	1,076,417
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	11,940	14,636
Consumer Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	351	1,034
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	571,451	574,054
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	412,339	409,237
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	77,503	77,456
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	9,159	9,230
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	71	73
Consumer Non-Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	5	7
Consumer Non-Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	7,614	7,712
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,382	1,415
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 87	$ 23