Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 2,867,013	$ 2,828,813
30-59 Days Past Due	10,278	14,303
60-89 Days Past Due	2,746	3,657
Loans > 90 Days And Accruing	1,072	2,037
Non- Accrual	38,971	53,399
Total Past Due & Non- Accrual	53,067	73,396
Total Loans	2,920,080	2,902,209
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	648,160	607,442
30-59 Days Past Due	720	2,628
60-89 Days Past Due	341	144
Loans > 90 Days And Accruing		170
Non- Accrual	8,543	12,195
Total Past Due & Non- Accrual	9,604	15,137
Total Loans	657,764	622,579
Agriculture production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	105,142	112,527
30-59 Days Past Due
60-89 Days Past Due
Loans > 90 Days And Accruing
Non- Accrual	33
Total Past Due & Non- Accrual	33
Total Loans	105,175	112,527
Real estate loans - Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	99,398	93,426
30-59 Days Past Due	19	399
60-89 Days Past Due
Non- Accrual	2,492	4,814
Total Past Due & Non- Accrual	2,511	5,213
Total Loans	101,909	98,639
Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,252,554	1,238,907
30-59 Days Past Due	4,424	3,276
60-89 Days Past Due	431	1,822
Loans > 90 Days And Accruing		65
Non- Accrual	15,352	22,612
Total Past Due & Non- Accrual	20,207	27,775
Total Loans	1,272,761	1,266,682
Real estate loans - Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	442,918	453,743
30-59 Days Past Due	3,828	5,734
60-89 Days Past Due	1,335	1,338
Loans > 90 Days And Accruing	879	1,246
Non- Accrual	11,148	11,476
Total Past Due & Non- Accrual	17,190	19,794
Total Loans	460,108	473,537
Real estate loans - Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	201,041	199,063
30-59 Days Past Due	755	1,467
60-89 Days Past Due	565	323
Loans > 90 Days And Accruing	193	556
Non- Accrual	1,234	1,997
Total Past Due & Non- Accrual	2,747	4,343
Total Loans	203,788	203,406
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	78,652	74,919
30-59 Days Past Due	532	799
60-89 Days Past Due	74	30
Loans > 90 Days And Accruing
Non- Accrual
Total Past Due & Non- Accrual	606	829
Total Loans	79,258	75,748
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,828	2,289
30-59 Days Past Due
Loans > 90 Days And Accruing
Non- Accrual		301
Total Past Due & Non- Accrual		301
Total Loans	1,828	2,590
Other Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	37,320	46,497
Non- Accrual	169	4
Total Past Due & Non- Accrual	169	4
Total Loans	$ 37,489	$ 46,501