Loans (Summary of Purchased Impaired and Nonimpaired Loans Acquired) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	$ 1,748,634	$ 1,633,331
Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	9,434	27,115
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	181,453	184,620
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	83,269	75,773
Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	324,870	247,494
Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	1,149,608	1,098,329
Non Impaired Purchased Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	1,736,303	1,629,141
Non Impaired Purchased Loans | Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	9,434	27,115
Non Impaired Purchased Loans | Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	181,453	184,389
Non Impaired Purchased Loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	82,700	75,773
Non Impaired Purchased Loans | Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	317,689	243,693
Non Impaired Purchased Loans | Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	1,145,027	1,098,171
Impaired Purchased Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	12,331	4,190
Impaired Purchased Loans | Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	0	0
Impaired Purchased Loans | Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	0	231
Impaired Purchased Loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	569	0
Impaired Purchased Loans | Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	7,181	3,801
Impaired Purchased Loans | Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	$ 4,581	$ 158