Loans and Leases (Loans and leases not covered by share agreements (past due financing receivables)) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 12,071	$ 7,173
60-89 Days Past Due	1,618	2,056
90 Days or More Past Due	454	0
Total Past Due	14,143	9,229
Current	2,746,374	2,772,785
Nonaccrual	32,356	43,156
Total	2,792,873	2,825,170
Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	7,026	2,774
60-89 Days Past Due	974	1,019
90 Days or More Past Due	404	0
Total Past Due	8,404	3,793
Current	1,959,956	1,967,571
Nonaccrual	22,458	30,128
Total	1,990,818	2,001,492
Agricultural Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,086	687
60-89 Days Past Due	10	0
90 Days or More Past Due	0	0
Total Past Due	1,096	687
Current	313,222	324,545
Nonaccrual	288	3,079
Total	314,606	328,311
Residential Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,006	1,278
60-89 Days Past Due	0	234
90 Days or More Past Due	0	0
Total Past Due	2,006	1,512
Current	232,241	241,860
Nonaccrual	6,206	6,317
Total	240,453	249,689
Consumer Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,953	2,434
60-89 Days Past Due	634	803
90 Days or More Past Due	50	0
Total Past Due	2,637	3,237
Current	240,955	238,809
Nonaccrual	3,404	3,632
Total	246,996	245,678
Commercial | Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	5,245	1,143
60-89 Days Past Due	624	525
90 Days or More Past Due	0	0
Total Past Due	5,869	1,668
Current	685,082	708,459
Nonaccrual	2,284	2,181
Total	693,235	712,308
Commercial Real Estate | Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,781	1,631
60-89 Days Past Due	350	494
90 Days or More Past Due	404	0
Total Past Due	2,535	2,125
Current	1,274,874	1,259,112
Nonaccrual	20,174	27,947
Total	$ 1,297,583	$ 1,289,184