Business and Summary of Significant Accounting Policies (Narrative) (Details)		3 Months Ended
	Jan. 01, 2020 USD ($)	Mar. 31, 2020 USD ($) branch
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period for which loans are considered past due		30 days
Minimum value of loans to be individually assessed for impairment		$ 500,000
Consumer Mortgage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period past due when loans go into non accrual status		90 days
Small Commercial Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period past due when loans go into non accrual status		90 days
Small Commercial Loans | Impaired Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum value of loans to be individually assessed for impairment		$ 500,000
Consumer Loan
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Delinquency period for loan charge offs		120 days
Retained Earnings | ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment, decrease in retained earnings	$ 82,400,000
Mutual of Omaha Bank ("MOB")
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Purchase price of acquisition	$ 993,100,000
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of branches | branch		90
Period past due when loans go into non accrual status		90 days
Minimum | Small Commercial Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Delinquency period for loan charge offs		90 days
Minimum | Small Commercial Loans | Impaired Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Delinquency period for loan charge offs		90 days
Maximum | Small Commercial Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Delinquency period for loan charge offs		150 days
Maximum | Small Commercial Loans | Impaired Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Delinquency period for loan charge offs		150 days