Loans (Summary of Purchased Impaired and Nonimpaired Loans Acquired) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	$ 1,633,331	$ 1,470,025
Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	27,115	1,242
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	184,620	174,123
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	75,773	51,292
Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	247,494	188,327
Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	1,098,329	1,055,041
Non Impaired Purchased Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	1,629,141	1,466,287
Non Impaired Purchased Loans | Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	27,115	1,242
Non Impaired Purchased Loans | Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	184,389	173,909
Non Impaired Purchased Loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	75,773	51,292
Non Impaired Purchased Loans | Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	243,693	187,375
Non Impaired Purchased Loans | Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	1,098,171	1,052,469
Impaired Purchased Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	4,190	3,738
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	231	214
Impaired Purchased Loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	0	0
Impaired Purchased Loans | Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	3,801	952
Impaired Purchased Loans | Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchased Loans	$ 158	$ 2,572