Loans and Leases (Loans and leases not covered by share agreements (past due financing receivables)) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 8,195	$ 8,380
60-89 Days Past Due	2,916	2,085
90 Days or More Past Due	0	24
Total Past Due	11,111	10,489
Current	3,538,074	3,447,226
Nonaccrual	31,928	42,394
Total	3,581,113	3,500,109
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	657	697
60-89 Days Past Due	919	741
90 Days or More Past Due	0	0
Total Past Due	1,576	1,438
Current	978,621	935,508
Nonaccrual	6,516	13,251
Total	986,713	950,197
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	3,363	3,042
60-89 Days Past Due	1,349	199
90 Days or More Past Due	0	24
Total Past Due	4,712	3,265
Current	1,543,649	1,511,618
Nonaccrual	12,551	14,800
Total	1,560,912	1,529,683
Commercial and Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	4,020	3,739
60-89 Days Past Due	2,268	940
90 Days or More Past Due	0	24
Total Past Due	6,288	4,703
Current	2,522,270	2,447,126
Nonaccrual	19,067	28,051
Total	2,547,625	2,479,880
Agricultural and Agricultural Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	417	818
60-89 Days Past Due	82	0
90 Days or More Past Due	0	0
Total Past Due	499	818
Current	364,791	369,907
Nonaccrual	5,058	6,010
Total	370,348	376,735
Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,580	1,199
60-89 Days Past Due	0	56
90 Days or More Past Due	0	0
Total Past Due	1,580	1,255
Current	358,051	342,735
Nonaccrual	5,531	5,359
Total	365,162	349,349
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,178	2,624
60-89 Days Past Due	566	1,089
90 Days or More Past Due	0	0
Total Past Due	2,744	3,713
Current	292,962	287,458
Nonaccrual	2,272	2,974
Total	$ 297,978	$ 294,145