Loans (Recorded Investment of Risk Category of Loans by Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 3,225,232		$ 3,081,973
Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,453,280	$ 1,500,247	1,495,862
Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	376,215	$ 384,654	384,526
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total			2,336,007
Pass | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Total			68
Pass | Acquired with Deteriorated Credit Quality | Loans Acquired In Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Total			254,629
Pass | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total			556,706
Pass | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,406,558		1,453,310
Pass | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	304,866		325,991
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total			99,228
Special Mention | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Total			613
Special Mention | Acquired with Deteriorated Credit Quality | Loans Acquired In Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Total			16,535
Special Mention | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total			19,671
Special Mention | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	27,319		30,504
Special Mention | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	58,274		49,053
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total			46,903
Substandard | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Total			11,060
Substandard | Acquired with Deteriorated Credit Quality | Loans Acquired In Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Total			12,769
Substandard | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total			15,026
Substandard | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	19,403		16,050
Substandard | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	13,075		15,827
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total			0
Doubtful | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Total			0
Doubtful | Acquired with Deteriorated Credit Quality | Loans Acquired In Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Total			0
Doubtful | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total			0
Doubtful | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0		0
Doubtful | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 0		0
Total
Financing Receivable, Credit Quality Indicator [Line Items]
Total			2,482,138
Total | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Total			11,741
Total | Acquired with Deteriorated Credit Quality | Loans Acquired In Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Total			283,933
Total | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total			591,403
Total | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total			1,499,864
Total | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total			$ 390,871