Loans and Leases (Loans and leases not covered by share agreements (credit quality indicator)) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013 loans	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 2,904,947	$ 2,825,170
Number of loans classified as doubtful	1
Number of loans classified as loss	0
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	755,658	712,308
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,287,337	1,289,184
Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,042,995	2,001,492
Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	324,339	328,311
Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	269,501	249,689
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	268,112	245,678
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,645,764	2,545,323
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	695,073	661,118
Pass | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,159,006	1,134,784
Pass | Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,854,079	1,795,902
Pass | Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	280,501	286,264
Pass | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	253,502	227,925
Pass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	257,682	235,232
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	259,183	279,847
Nonpass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	60,585	51,190
Nonpass | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	128,331	154,400
Nonpass | Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	188,916	205,590
Nonpass | Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	43,838	42,047
Nonpass | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	15,999	21,764
Nonpass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 10,430	$ 10,446