Loans and Leases (Loans and leases not covered by share agreements (credit quality indicator)) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	$ 5,506,408	$ 5,003,866
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	1,295,504	1,279,214
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	2,555,268	2,326,360
Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	3,850,772	3,605,574
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	471,271	471,870
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	753,666	539,555
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	430,699	386,867
Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	5,041,241	4,541,863
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	1,128,858	1,106,276
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	2,339,414	2,107,474
Pass | Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	3,468,272	3,213,750
Pass | Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	426,929	435,745
Pass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	725,773	515,195
Pass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	420,267	377,173
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	465,167	462,003
Nonpass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	166,646	172,938
Nonpass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	215,854	218,886
Nonpass | Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	382,500	391,824
Nonpass | Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	44,342	36,125
Nonpass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	27,893	24,360
Nonpass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	$ 10,432	$ 9,694