Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 2,881,605	$ 2,828,813
30-59 Days Past Due	5,846	14,303
60-89 Days Past Due	2,177	3,657
Loans > 90 Days And Accruing	837	2,037
Non- Accrual	34,992	53,399
Total Past Due & Non- Accrual	43,852	73,396
Total Loans	2,925,457	2,902,209
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	645,044	607,442
30-59 Days Past Due	845	2,628
60-89 Days Past Due		144
Loans > 90 Days And Accruing		170
Non- Accrual	6,467	12,195
Total Past Due & Non- Accrual	7,312	15,137
Total Loans	652,356	622,579
Agriculture production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	98,458	112,527
30-59 Days Past Due
60-89 Days Past Due
Loans > 90 Days And Accruing
Non- Accrual	31
Total Past Due & Non- Accrual	31
Total Loans	98,489	112,527
Real estate loans - Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	147,157	93,426
30-59 Days Past Due		399
60-89 Days Past Due
Loans > 90 Days And Accruing	75
Non- Accrual	2,643	4,814
Total Past Due & Non- Accrual	2,718	5,213
Total Loans	149,875	98,639
Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,246,319	1,238,907
30-59 Days Past Due	843	3,276
60-89 Days Past Due	831	1,822
Loans > 90 Days And Accruing		65
Non- Accrual	16,187	22,612
Total Past Due & Non- Accrual	17,861	27,775
Total Loans	1,264,180	1,266,682
Real estate loans - Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	439,860	453,743
30-59 Days Past Due	2,627	5,734
60-89 Days Past Due	998	1,338
Loans > 90 Days And Accruing	417	1,246
Non- Accrual	8,375	11,476
Total Past Due & Non- Accrual	12,417	19,794
Total Loans	452,277	473,537
Real estate loans - Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	204,028	199,063
30-59 Days Past Due	1,153	1,467
60-89 Days Past Due	260	323
Loans > 90 Days And Accruing	282	556
Non- Accrual	1,093	1,997
Total Past Due & Non- Accrual	2,788	4,343
Total Loans	206,816	203,406
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	69,819	74,919
30-59 Days Past Due	378	799
60-89 Days Past Due	88	30
Loans > 90 Days And Accruing	63
Non- Accrual	32		32
Total Past Due & Non- Accrual	561	829
Total Loans	70,380	75,748
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,815	2,289
30-59 Days Past Due
Loans > 90 Days And Accruing
Non- Accrual		301
Total Past Due & Non- Accrual		301
Total Loans	1,815	2,590
Other Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	29,105	46,497
Non- Accrual	164	4
Total Past Due & Non- Accrual	164	4
Total Loans	$ 29,269	$ 46,501