Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 3,648,461	$ 3,549,125
30-59 Days Past Due	14,772	16,864
60-89 Days Past Due	7,076	8,668
Loans 90 Days And Accruing	1,135	1,350
Non-Accrual	51,289	56,402
Total Past Due & Non-Accrual	74,272	83,284
Total	3,722,733	3,632,409
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	842,996	749,020
30-59 Days Past Due	5,403	2,628
60-89 Days Past Due	2,045	774
Non-Accrual	7,400	9,283
Total Past Due & Non-Accrual	14,848	12,685
Total	857,844	761,705
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	101,864	114,305
30-59 Days Past Due	380	13
Non-Accrual	26	30
Total Past Due & Non-Accrual	406	43
Total	102,270	114,348
Real estate loans - Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	161,867	171,046
30-59 Days Past Due	473	1,058
Loans 90 Days And Accruing	134
Non-Accrual	2,914	4,978
Total Past Due & Non-Accrual	3,521	6,036
Total	165,388	177,082
Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,589,583	1,573,403
30-59 Days Past Due	3,968	3,807
60-89 Days Past Due	2,792	5,801
Loans 90 Days And Accruing	90	703
Non-Accrual	25,003	28,095
Total Past Due & Non-Accrual	31,853	38,406
Total	1,621,436	1,611,809
Real estate loans - Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	610,191	595,192
30-59 Days Past Due	3,392	7,156
60-89 Days Past Due	1,449	1,475
Loans 90 Days And Accruing	787	494
Non-Accrual	13,343	12,068
Total Past Due & Non-Accrual	18,971	21,193
Total	629,162	616,385
Real estate loans - Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	257,791	251,188
30-59 Days Past Due	733	1,652
60-89 Days Past Due	736	563
Loans 90 Days And Accruing	118	153
Non-Accrual	2,433	1,667
Total Past Due & Non-Accrual	4,020	4,035
Total	261,811	255,223
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	60,880	69,061
30-59 Days Past Due	423	550
60-89 Days Past Due	54	55
Loans 90 Days And Accruing	6
Non-Accrual	170	117
Total Past Due & Non-Accrual	653	722
Total	61,533	69,783
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,231	1,545
Total	1,231	1,545
Other loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,058	24,365
30-59 Days Past Due
Non-Accrual		164
Total Past Due & Non-Accrual		164
Total	$ 22,058	$ 24,529