Loans and Leases (Loans and leases not covered by share agreements (credit quality indicator)) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	$ 5,484,759	$ 5,003,866
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	1,287,301	1,279,214
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	2,643,578	2,326,360
Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	3,930,879	3,605,574
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	480,883	471,870
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	644,267	539,555
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	428,730	386,867
Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	5,058,438	4,541,863
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	1,154,318	1,106,276
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	2,438,572	2,107,474
Pass | Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	3,592,890	3,213,750
Pass | Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	431,671	435,745
Pass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	615,626	515,195
Pass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	418,251	377,173
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	426,321	462,003
Nonpass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	132,983	172,938
Nonpass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	205,006	218,886
Nonpass | Commercial and commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	337,989	391,824
Nonpass | Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	49,212	36,125
Nonpass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	28,641	24,360
Nonpass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total gross loans and leases receivable held to maturity	$ 10,479	$ 9,694