Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 3,534,935	$ 3,549,125
30-59 Days Past Due	17,783	16,864
60-89 Days Past Due	6,514	8,668
Loans 90 Days And Accruing	1,709	1,350
Non-Accrual	55,686	56,402
Total Past Due & Non-Accrual	81,692	83,284
Total	3,616,627	3,632,409
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	776,473	749,020
30-59 Days Past Due	1,933	2,628
60-89 Days Past Due	426	774
Non-Accrual	8,558	9,283
Total Past Due & Non-Accrual	10,917	12,685
Total	787,390	761,705
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	99,198	114,305
30-59 Days Past Due		13
Non-Accrual	28	30
Total Past Due & Non-Accrual	28	43
Total	99,226	114,348
Real estate loans - Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	151,645	171,046
30-59 Days Past Due	400	1,058
Non-Accrual	3,072	4,978
Total Past Due & Non-Accrual	3,472	6,036
Total	155,117	177,082
Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,561,328	1,573,403
30-59 Days Past Due	10,941	3,807
60-89 Days Past Due	4,700	5,801
Loans 90 Days And Accruing	1,168	703
Non-Accrual	28,598	28,095
Total Past Due & Non-Accrual	45,407	38,406
Total	1,606,735	1,611,809
Real estate loans - Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	608,917	595,192
30-59 Days Past Due	3,236	7,156
60-89 Days Past Due	663	1,475
Loans 90 Days And Accruing	448	494
Non-Accrual	12,938	12,068
Total Past Due & Non-Accrual	17,285	21,193
Total	626,202	616,385
Real estate loans - Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	252,734	251,188
30-59 Days Past Due	932	1,652
60-89 Days Past Due	684	563
Loans 90 Days And Accruing	89	153
Non-Accrual	2,351	1,667
Total Past Due & Non-Accrual	4,056	4,035
Total	256,790	255,223
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	61,216	69,061
30-59 Days Past Due	340	550
60-89 Days Past Due	41	55
Loans 90 Days And Accruing	4
Non-Accrual	141	117
Total Past Due & Non-Accrual	526	722
Total	61,742	69,783
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,378	1,545
Non-Accrual
Total	1,378	1,545
Other loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,046	24,365
30-59 Days Past Due	1
Non-Accrual		164
Total Past Due & Non-Accrual	1	164
Total	$ 22,047	$ 24,529