Loans (Risk Category of Loans by Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 3,091,998		$ 3,081,973
Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,467,397	$ 1,500,247	1,495,862
Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	376,186	$ 384,654	384,526
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			2,336,007
Pass | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			68
Pass | Acquired with Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			254,629
Pass | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			556,706
Pass | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,370,614		1,453,310
Pass | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	301,807		325,991
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			99,228
Special Mention | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			613
Special Mention | Acquired with Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			16,535
Special Mention | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			19,671
Special Mention | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	76,984		30,504
Special Mention | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	62,442		49,053
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			46,903
Substandard | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			11,060
Substandard | Acquired with Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			12,769
Substandard | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			15,026
Substandard | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	19,799		16,050
Substandard | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	11,937		15,827
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			0
Doubtful | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			0
Doubtful | Acquired with Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			0
Doubtful | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			0
Doubtful | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0		0
Doubtful | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0		0
Total
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			2,482,138
Total | Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			11,741
Total | Acquired with Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			283,933
Total | Commercial and Industrial Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			591,403
Total | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			1,499,864
Total | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans			$ 390,871