Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 6,483,448	$ 5,139,645
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,436,092	1,194,646
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	117,751	79,689
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	498,862	418,703
Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,571,253	1,953,062
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	938,437	739,169
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	502,240	418,525
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	86,406	77,479
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	3,877	311
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	328,530	258,061
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	4,843,433	3,769,920
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,366,945	1,117,545
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	64,699	30,712
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	469,967	398,646
Commercial Pass | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,409,972	1,811,367
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	175,260	146,251
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	25,610	7,310
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	3,497	228
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	327,483	257,861
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	149,567	124,863
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	43,245	30,919
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	29,765	25,273
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,619	3,490
Commercial Special Mention | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	70,397	60,028
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,161	5,106
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans		47
Commercial Special Mention | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	380
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	139,898	159,215
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	25,234	46,182
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	22,516	23,704
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	986	1,858
Commercial Substandard | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	85,732	80,626
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,259	6,046
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	124	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	1,047	200
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	3,527
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	668
Commercial Doubtful | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	622
Commercial Doubtful | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,976
Commercial Doubtful | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	149
Commercial Doubtful | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	112
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans
Commercial Loss | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,333,995	1,076,417
Consumer Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	149
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	26,155	14,636
Consumer Performing | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	3,173	1,034
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	743,713	574,054
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	474,465	409,237
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	86,340	77,456
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	13,028	9,230
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	135	73
Consumer Non-Performing | Real estate loans - Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	3	7
Consumer Non-Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	10,895	7,712
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,929	1,415
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 66	$ 23