Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	$ 8,427,414	$ 7,186,609
Loans 90 Days or More Past Due And Accruing	69	1,855
Non-Accrual	15,949	26,148
Total Past Due & Non-Accrual	31,896	37,858
Total	8,459,310	7,224,467
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	14,683	8,794
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	1,195	1,061
Commercial and industrial loans
Financing Receivable, Past Due [Line Items]
Current	2,105,445	1,723,337
Loans 90 Days or More Past Due And Accruing	4	249
Non-Accrual	1,255	1,803
Total Past Due & Non-Accrual	4,434	3,327
Total	2,109,879	1,726,664
Commercial and industrial loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	3,039	1,093
Commercial and industrial loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	136	182
Agricultural production financing and other loans to farmers
Financing Receivable, Past Due [Line Items]
Current	93,678	89,440
Loans 90 Days or More Past Due And Accruing	0	0
Non-Accrual	183	679
Total Past Due & Non-Accrual	183	2,964
Total	93,861	92,404
Agricultural production financing and other loans to farmers | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	2,285
Agricultural production financing and other loans to farmers | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Construction
Financing Receivable, Past Due [Line Items]
Current	784,961	535,520
Loans 90 Days or More Past Due And Accruing	0	1,478
Non-Accrual	977	8,667
Total Past Due & Non-Accrual	2,607	10,209
Total	787,568	545,729
Construction | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	1,630	64
Construction | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Commercial and farmland
Financing Receivable, Past Due [Line Items]
Current	3,043,318	2,822,515
Loans 90 Days or More Past Due And Accruing	0	0
Non-Accrual	7,007	8,156
Total Past Due & Non-Accrual	9,380	9,587
Total	3,052,698	2,832,102
Commercial and farmland | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	2,324	1,253
Commercial and farmland | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	49	178
Residential
Financing Receivable, Past Due [Line Items]
Current	1,133,476	959,252
Loans 90 Days or More Past Due And Accruing	22	17
Non-Accrual	5,062	4,966
Total Past Due & Non-Accrual	9,741	7,169
Total	1,143,217	966,421
Residential | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	4,290	1,756
Residential | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	367	430
Home equity
Financing Receivable, Past Due [Line Items]
Current	584,023	524,198
Loans 90 Days or More Past Due And Accruing	42	107
Non-Accrual	1,421	1,481
Total Past Due & Non-Accrual	4,961	3,959
Total	588,984	528,157
Home equity | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	2,960	2,164
Home equity | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	538	207
Consumer
Financing Receivable, Past Due [Line Items]
Current	135,399	99,499
Loans 90 Days or More Past Due And Accruing	1	4
Non-Accrual	44	42
Total Past Due & Non-Accrual	590	289
Total	135,989	99,788
Consumer | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	440	179
Consumer | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	105	64
Public finance and other commercial loans
Financing Receivable, Past Due [Line Items]
Current	547,114	432,848
Loans 90 Days or More Past Due And Accruing	0	0
Non-Accrual	0	354
Total Past Due & Non-Accrual	0	354
Total	547,114	433,202
Public finance and other commercial loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Public finance and other commercial loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	$ 0	$ 0