Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 5,613,144	$ 5,139,645
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,289,884	1,194,646
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	75,746	79,689
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	442,389	418,703
Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,167,729	1,953,062
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	847,580	739,169
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	436,038	418,525
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	79,887	77,479
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	232	311
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	273,659	258,061
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	4,193,877	3,769,920
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,235,039	1,117,545
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	33,917	30,712
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	414,112	398,646
Commercial Pass | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,050,396	1,811,367
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	175,169	146,251
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	11,847	7,310
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	232	228
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	273,165	257,861
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	101,954	124,863
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	19,811	30,919
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	25,818	25,273
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	5,471	3,490
Commercial Special Mention | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	47,526	60,028
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	3,298	5,106
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	30	47
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	124,442	159,215
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	35,034	46,182
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	16,011	23,704
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,059	1,858
Commercial Substandard | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	67,681	80,626
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,069	6,046
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	94	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	494	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	91
Commercial Loss | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	91
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,181,405	1,076,417
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	21,678	14,636
Consumer Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	343	1,034
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	656,576	574,054
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	422,979	409,237
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	79,829	77,456
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	9,688	9,230
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	69	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	8,468	7,712
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,088	1,415
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 58	$ 23