Summary of Significant Accounting Policies (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($) Payment Quarter	Dec. 31, 2017 USD ($)
New Accounting Standards [Abstract]
Equity securities		$ 25.0
Unrealized holding loss on securities		$ (0.6)
Federal corporate income tax rate	21.00%
Loans [Abstract]
Past due period after which loans must be well secured and in the process of collection to continue accruing interest	90 days
Period of current principal and interest payments for reclassifying nonaccrual loans as accruing loans	6 months
Allowance for Loan and Lease Losses [Abstract]
Number of delinquent monthly payments before loan charge off \| Payment	5
Threshold period past due for initiation of foreclosure proceedings	120 days
Current value assessment period for past due loans secured against real estate	90 days
Historical loan loss review period \| Quarter	12
Minimum [Member]
New Accounting Standards [Abstract]
Net present value of all potential lease payments	$ 10.1
Other Real Estate Owned [Abstract]
Typical frequency of periodic reviews	12 months
Maximum [Member]
New Accounting Standards [Abstract]
Net present value of all potential lease payments	$ 20.3
Other Real Estate Owned [Abstract]
Typical frequency of periodic reviews	18 months
Frequency of periodic reviews in general	24 months
Commercial [Member] \| Unsecured Commercial Loan [Member]
Allowance for Loan and Lease Losses [Abstract]
Charge off threshold for loans considered uncollectible	90 days
Consumer [Member] \| Closed-End Consumer Loan [Member]
Allowance for Loan and Lease Losses [Abstract]
Charge off threshold for loans considered uncollectible	120 days

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Refer to current value assessment period for past due loans secured against real estate, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of quarters over which historical loss rates are generally reviewed.

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The maximum number of delinquent payments that a closed-end loan (excluding conventional 1-4 family residential loans and installment and revolving loans secured by real estate) may be delinquent before being charged-off. If a loan is considered uncollectable, it is charged off earlier.

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The frequency of periodic reviews for appraisals on foreclosed properties and other real estate owned generally, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The typical frequency of periodic reviews for appraisals on foreclosed properties and other real estate owned, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Refers to the past due period after which loans must be well secured and in the process of collection to continue accruing interest, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period for which principal and interest payments must remain current for reclassifying nonaccrual loans as accruing loans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Threshold period past due for the initiation of foreclosure proceedings, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments for other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Present value of minimum lease payments for capital leases net of executory costs, including amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Threshold period past due for financing receivable to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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