Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 8,299,260	$ 7,224,467
Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,034,311	1,726,664
Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	90,462	92,404
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	670,138	545,729
Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,144,649	2,832,102
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,155,403	966,421
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	601,335	528,157
Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	131,246	99,788
Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	471,716	433,202
Commercial Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,296,426	5,528,751
Commercial Pass | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,923,043	1,660,879
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	70,715	78,446
Commercial Pass | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	638,040	492,358
Commercial Pass | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,963,113	2,669,491
Commercial Pass | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	198,986	170,075
Commercial Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	30,813	24,653
Commercial Pass | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Pass | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	471,716	432,849
Commercial Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	145,230	115,342
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	62,219	23,246
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,681	5,966
Commercial Special Mention | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	288	2,185
Commercial Special Mention | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	73,429	76,037
Commercial Special Mention | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,492	7,373
Commercial Special Mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	121	535
Commercial Special Mention | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Special Mention | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	173,496	161,929
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	48,719	42,539
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	13,867	7,992
Commercial Substandard | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,818	24,224
Commercial Substandard | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	101,025	84,288
Commercial Substandard | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,195	2,076
Commercial Substandard | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	872	457
Commercial Substandard | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Substandard | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	353
Commercial Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	329	0
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	329	0
Commercial Doubtful | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Doubtful | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1	0
Commercial Loss | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1	0
Commercial Loss | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial Loss | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,676,894	1,410,521
Consumer Performing | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	199	0
Consumer Performing | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	29,992	25,419
Consumer Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,082	2,285
Consumer Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	940,613	782,080
Consumer Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	567,865	500,996
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	131,143	99,741
Consumer Performing | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,884	7,924
Consumer Non-Performing | Commercial and industrial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing | Agricultural production financing and other loans to farmers
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer Non-Performing | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	1,543
Consumer Non-Performing | Commercial and farmland
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	1
Consumer Non-Performing | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,117	4,817
Consumer Non-Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,664	1,516
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	103	47
Consumer Non-Performing | Public finance and other commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0