Loans and Leases (Loans and leases not covered by share agreements (past due financing receivables)) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 6,663	$ 7,173
60-89 Days Past Due	2,063	2,056
90 Days or More Past Due	6	0
Total Past Due	8,732	9,229
Current	2,786,067	2,772,785
Nonaccrual	41,003	43,156
Total	2,835,802	2,825,170
Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,020	2,774
60-89 Days Past Due	853	1,019
90 Days or More Past Due	0	0
Total Past Due	2,873	3,793
Current	1,977,596	1,967,571
Nonaccrual	24,414	30,128
Total	2,004,883	2,001,492
Agricultural Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	304	687
60-89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total Past Due	304	687
Current	319,907	324,545
Nonaccrual	7,279	3,079
Total	327,490	328,311
Residential Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,374	1,278
60-89 Days Past Due	629	234
90 Days or More Past Due	0	0
Total Past Due	2,003	1,512
Current	240,608	241,860
Nonaccrual	5,993	6,317
Total	248,604	249,689
Consumer Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,965	2,434
60-89 Days Past Due	581	803
90 Days or More Past Due	6	0
Total Past Due	3,552	3,237
Current	247,956	238,809
Nonaccrual	3,317	3,632
Total	254,825	245,678
Commercial | Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	603	1,143
60-89 Days Past Due	98	525
90 Days or More Past Due	0	0
Total Past Due	701	1,668
Current	702,979	708,459
Nonaccrual	6,228	2,181
Total	709,908	712,308
Commercial Real Estate | Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,417	1,631
60-89 Days Past Due	755	494
90 Days or More Past Due	0	0
Total Past Due	2,172	2,125
Current	1,274,617	1,259,112
Nonaccrual	18,186	27,947
Total	$ 1,294,975	$ 1,289,184