Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 7,186,609	$ 6,703,256
Loans 90 Days or More Past Due And Accruing	1,855	924
Non-Accrual	26,148	28,724
Total Past Due & Non-Accrual	37,858	47,943
Total	7,224,467	6,751,199
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8,794	16,773
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,061	1,522
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,723,337	1,487,221
Loans 90 Days or More Past Due And Accruing	249
Non-Accrual	1,803	3,275
Total Past Due & Non-Accrual	3,327	6,272
Total	1,726,664	1,493,493
Commercial and industrial loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,093	2,967
Commercial and industrial loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	182	30
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	89,440	120,720
Loans 90 Days or More Past Due And Accruing
Non-Accrual	679	1,027
Total Past Due & Non-Accrual	2,964	1,037
Total	92,404	121,757
Agricultural production financing and other loans to farmers | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,285	10
Agricultural production financing and other loans to farmers | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	535,520	610,896
Loans 90 Days or More Past Due And Accruing	1,478	65
Non-Accrual	8,667	65
Total Past Due & Non-Accrual	10,209	1,323
Total	545,729	612,219
Construction | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	64	1,193
Construction | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due
Commercial and farmland
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,822,515	2,542,048
Loans 90 Days or More Past Due And Accruing		603
Non-Accrual	8,156	12,951
Total Past Due & Non-Accrual	9,587	20,643
Total	2,832,102	2,562,691
Commercial and farmland | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,253	6,923
Commercial and farmland | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	178	166
Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	959,252	948,947
Loans 90 Days or More Past Due And Accruing	17	56
Non-Accrual	4,966	9,444
Total Past Due & Non-Accrual	7,169	13,818
Total	966,421	962,765
Residential | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,756	4,010
Residential | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	430	308
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	524,198	510,362
Loans 90 Days or More Past Due And Accruing	107	175
Non-Accrual	1,481	1,928
Total Past Due & Non-Accrual	3,959	3,659
Total	528,157	514,021
Home equity | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,164	1,372
Home equity | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	207	184
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	99,499	85,744
Loans 90 Days or More Past Due And Accruing	4	25
Non-Accrual	42	34
Total Past Due & Non-Accrual	289	1,191
Total	99,788	86,935
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	179	298
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	64	834
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,600	2,527
Non-Accrual
Total Past Due & Non-Accrual
Total	1,600	2,527
Other commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	431,248	394,791
Non-Accrual	354
Total Past Due & Non-Accrual	354
Total	431,602	394,791
Other commercial loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due