Loans and Leases (Loans and leases not covered by share agreements (credit quality indicator)) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 2,835,802	$ 2,825,170
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,558,927	2,545,323
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	276,875	279,847
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,004,883	2,001,492
Commercial Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,802,830	1,795,902
Commercial Portfolio Segment | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	202,053	205,590
Agricultural Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	327,490	328,311
Agricultural Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	281,217	286,264
Agricultural Portfolio Segment | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	46,273	42,047
Residential Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	248,604	249,689
Residential Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	230,338	227,925
Residential Portfolio Segment | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	18,266	21,764
Consumer Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	254,825	245,678
Consumer Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	244,542	235,232
Consumer Portfolio Segment | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	10,283	10,446
Commercial | Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	709,908	712,308
Commercial | Commercial Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	653,984	661,118
Commercial | Commercial Portfolio Segment | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	55,924	51,190
Commercial Real Estate | Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,294,975	1,289,184
Commercial Real Estate | Commercial Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,148,846	1,134,784
Commercial Real Estate | Commercial Portfolio Segment | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 146,129	$ 154,400