Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 7,224,467	$ 6,751,199
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,726,664	1,493,493
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	92,404	121,757
Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	545,729	612,219
Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,832,102	2,562,691
Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	966,421	962,765
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	528,157	514,021
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	99,788	86,935
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	1,600	2,527
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	431,602	394,791
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,528,751	5,099,464
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,660,879	1,418,401
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	78,446	73,800
Commercial Pass | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	492,358	587,906
Commercial Pass | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,669,491	2,408,329
Commercial Pass | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	170,075	185,725
Commercial Pass | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	24,653	28,554
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	1,600	2,527
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	431,249	394,222
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	115,342	154,573
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	23,246	51,336
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	5,966	27,502
Commercial Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	2,185	828
Commercial Special Mention | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	76,037	70,074
Commercial Special Mention | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	7,373	4,376
Commercial Special Mention | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	535	457
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	161,929	129,218
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	42,539	23,386
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	7,992	20,018
Commercial Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	24,224	981
Commercial Substandard | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	84,288	79,769
Commercial Substandard | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	2,076	4,209
Commercial Substandard | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	457	286
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans
Commercial Substandard | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	353	569
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans		2,407
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans		370
Commercial Doubtful | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans		387
Commercial Doubtful | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans		1,536
Commercial Doubtful | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans		114
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans		50
Commercial Loss | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans		50
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,410,521	1,354,790
Consumer Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	25,419	22,374
Consumer Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,285	2,980
Consumer Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	782,080	759,900
Consumer Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	500,996	482,661
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	99,741	86,875
Consumer Non Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	7,924	10,697
Consumer Non Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,543	130
Consumer Non Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1	3
Consumer Non Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,817	8,441
Consumer Non Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,516	2,063
Consumer Non Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 47	$ 60