Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 3,772,467	$ 3,632,409
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	900,970	761,705
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	99,649	114,348
Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	178,213	177,082
Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment [Line Items]
Loans	1,603,698	1,611,809
Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	625,609	616,385
Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	269,952	255,223
Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	66,832	69,783
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	1,208	1,545
Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans	26,336	24,529
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,725,512	2,635,448
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	835,214	708,835
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	83,753	114,318
Commercial Pass | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	153,293	162,976
Commercial Pass | Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment [Line Items]
Loans	1,480,054	1,473,714
Commercial Pass | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	139,702	143,657
Commercial Pass | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	6,068	6,194
Commercial Pass | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	1,095	1,420
Commercial Pass | Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans	26,333	24,334
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	62,026	72,407
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	15,803	11,332
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	1,957
Commercial Special Mention | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,584	1,132
Commercial Special Mention | Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment [Line Items]
Loans	40,232	57,676
Commercial Special Mention | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	2,181	2,232
Commercial Special Mention | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	266	35
Commercial Special Mention | Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans	3
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	163,167	146,254
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	49,658	41,013
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	13,939	30
Commercial Substandard | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	8,606	12,029
Commercial Substandard | Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment [Line Items]
Loans	83,177	80,184
Commercial Substandard | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	7,227	11,494
Commercial Substandard | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	447	1,184
Commercial Substandard | Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment [Line Items]
Loans	113	125
Commercial Substandard | Other loans
Financing Receivable, Recorded Investment [Line Items]
Loans		195
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	295	661
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	295	525
Commercial Doubtful | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans		136
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	807,398	764,261
Consumer Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	14,581
Consumer Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	464,912	448,494
Consumer Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	261,316	246,101
Consumer Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	66,589	69,666
Consumer Non-Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	14,069	13,378
Consumer Non-Performing | Real estate loans - Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	149	945
Consumer Non-Performing | Real estate loans - Commercial and farm land
Financing Receivable, Recorded Investment [Line Items]
Loans	235	235
Consumer Non-Performing | Real estate loans - Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	11,587	10,372
Consumer Non-Performing | Real estate loans - Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	1,855	1,709
Consumer Non-Performing | Individuals' loans for household and other personal expenditures
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 243	$ 117