Loans and Leases (Loans and leases not covered by share agreements (credit quality indicator)) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014 loans	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 3,581,113	$ 3,500,109
Number of loans classified as loss	0
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	986,713	950,197
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,560,912	1,529,683
Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,547,625	2,479,880
Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	370,348	376,735
Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	365,162	349,349
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	297,978	294,145
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	3,258,337	3,215,775
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	896,019	871,825
Pass | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,401,965	1,390,820
Pass | Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,297,984	2,262,645
Pass | Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	330,764	335,821
Pass | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	340,936	333,161
Pass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	288,653	284,148
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	322,776	284,334
Nonpass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	90,694	78,372
Nonpass | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	158,947	138,863
Nonpass | Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	249,641	217,235
Nonpass | Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	39,584	40,914
Nonpass | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	24,226	16,188
Nonpass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 9,325	$ 9,997