Loans (Not Covered by Share Agreements (Credit Quality Indicator)) (Details) $ in Thousands	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Number of loans classified as doubtful | loan	0
Number of loans classified as loss | loan	0
Loans and leases receivable	$ 8,373,497	$ 7,410,881
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	7,816,728	6,947,494
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	556,769	463,387
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	6,790,458	5,731,712
Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	6,392,551	5,404,923
Commercial | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	397,907	326,789
Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,419,909	2,020,231
Commercial | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,251,115	1,880,579
Commercial | Commercial | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	168,794	139,652
Commercial | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	4,370,549	3,711,481
Commercial | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	4,141,436	3,524,344
Commercial | Commercial real estate | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	229,113	187,137
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	533,064	565,408
Agricultural and agricultural real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	415,455	471,642
Agricultural and agricultural real estate | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	117,609	93,766
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	597,742	673,603
Residential real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	569,401	645,478
Residential real estate | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	28,341	28,125
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	452,233	440,158
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	439,321	425,451
Consumer | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 12,912	$ 14,707