Loans (Not Covered by Share Agreements (Credit Quality Indicator)) (Details) $ in Thousands	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($)
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	$ 7,410,881	$ 6,393,226
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	6,947,494	6,009,382
Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	463,387	383,844
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	5,731,712	4,809,875
Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	5,404,923	4,538,284
Commercial | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	326,789	271,591
Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	2,020,231	1,646,606
Commercial | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	1,880,579	1,552,783
Commercial | Commercial | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	139,652	93,823
Commercial | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	3,711,481	3,163,269
Commercial | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	3,524,344	2,985,501
Commercial | Commercial real estate | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	187,137	177,768
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	565,408	511,588
Agricultural and agricultural real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	471,642	451,539
Agricultural and agricultural real estate | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	93,766	60,049
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	673,603	624,279
Residential real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	645,478	586,623
Residential real estate | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	28,125	37,656
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	440,158	447,484
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	425,451	432,936
Consumer | Nonpass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable	$ 14,707	$ 14,548