Loans and Leases (Loans and leases not covered by share agreements (credit quality indicator)) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 4,451,294	$ 3,877,863
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,189,626	1,036,080
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,010,091	1,707,060
Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	3,199,717	2,743,140
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	444,110	423,827
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	443,026	380,341
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	364,441	330,555
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	4,108,825	3,592,750
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,071,508	939,717
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,834,875	1,567,711
Pass | Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,906,383	2,507,428
Pass | Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	422,208	402,883
Pass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	424,365	361,325
Pass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	355,869	321,114
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	342,469	285,113
Nonpass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	118,118	96,363
Nonpass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	175,216	139,349
Nonpass | Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	293,334	235,712
Nonpass | Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	21,902	20,944
Nonpass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	18,661	19,016
Nonpass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 8,572	$ 9,441