Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 8,482,975	$ 8,427,414
Non-Accrual	15,649	15,949
Total Past Due & Non-Accrual	123,874	31,896
Total	8,606,849	8,459,310
Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Current	2,175,423	2,105,445
Non-Accrual	1,759	1,255
Total Past Due & Non-Accrual	23,803	4,434
Total	2,199,226	2,109,879
Agricultural production financing and other loans to farmers
Financing Receivable, Past Due [Line Items]
Current	86,566	93,678
Non-Accrual	0	183
Total Past Due & Non-Accrual	855	183
Total	87,421	93,861
Construction
Financing Receivable, Past Due [Line Items]
Current	622,171	784,961
Non-Accrual	1,094	977
Total Past Due & Non-Accrual	21,503	2,607
Total	643,674	787,568
Commercial and farmland
Financing Receivable, Past Due [Line Items]
Current	3,204,303	3,043,318
Non-Accrual	6,995	7,007
Total Past Due & Non-Accrual	63,865	9,380
Total	3,268,168	3,052,698
Residential
Financing Receivable, Past Due [Line Items]
Current	1,112,523	1,133,476
Non-Accrual	4,332	5,062
Total Past Due & Non-Accrual	9,033	9,741
Total	1,121,556	1,143,217
Home equity
Financing Receivable, Past Due [Line Items]
Current	566,018	584,023
Non-Accrual	1,409	1,421
Total Past Due & Non-Accrual	4,380	4,961
Total	570,398	588,984
Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Current	129,330	135,399
Non-Accrual	60	44
Total Past Due & Non-Accrual	435	590
Total	129,765	135,989
Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Current	586,641	547,114
Non-Accrual	0	0
Total Past Due & Non-Accrual	0
Total	586,641	547,114
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	100,677	14,683
30-59 Days Past Due | Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Past Due	21,717	3,039
30-59 Days Past Due | Agricultural production financing and other loans to farmers
Financing Receivable, Past Due [Line Items]
Past Due	855	0
30-59 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Past Due	19,542	1,630
30-59 Days Past Due | Commercial and farmland
Financing Receivable, Past Due [Line Items]
Past Due	51,516	2,324
30-59 Days Past Due | Residential
Financing Receivable, Past Due [Line Items]
Past Due	4,536	4,290
30-59 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Past Due	2,191	2,960
30-59 Days Past Due | Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Past Due	320	440
30-59 Days Past Due | Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	7,236	1,195
60-89 Days Past Due | Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Past Due	119	136
60-89 Days Past Due | Agricultural production financing and other loans to farmers
Financing Receivable, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Past Due	867	0
60-89 Days Past Due | Commercial and farmland
Financing Receivable, Past Due [Line Items]
Past Due	5,354	49
60-89 Days Past Due | Residential
Financing Receivable, Past Due [Line Items]
Past Due	133	367
60-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Past Due	708	538
60-89 Days Past Due | Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Past Due	55	105
60-89 Days Past Due | Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Loans 90 Days or More Past Due And Accruing
Financing Receivable, Past Due [Line Items]
Past Due	312	69
Loans 90 Days or More Past Due And Accruing | Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Past Due	208	4
Loans 90 Days or More Past Due And Accruing | Agricultural production financing and other loans to farmers
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Loans 90 Days or More Past Due And Accruing | Construction
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Loans 90 Days or More Past Due And Accruing | Commercial and farmland
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Loans 90 Days or More Past Due And Accruing | Residential
Financing Receivable, Past Due [Line Items]
Past Due	32	22
Loans 90 Days or More Past Due And Accruing | Home equity
Financing Receivable, Past Due [Line Items]
Past Due	72	42
Loans 90 Days or More Past Due And Accruing | Individuals' loans for household and other personal expenditures
Financing Receivable, Past Due [Line Items]
Past Due	0	1
Loans 90 Days or More Past Due And Accruing | Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Past Due	$ 0	$ 0