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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 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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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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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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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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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of amortization of purchase premium on nonoperating securities.

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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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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Accounting Policies (Details) $ in Thousands	3 Months Ended	12 Months Ended
Accounting Policies (Details) $ in Thousands	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) Payment Quarter Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Certificates of Deposits in Other Banks [Abstract]
Maturity period of certificates of deposit in other banks			18 months
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
Current value assessment period for past due loans secured against real estate			90 days
Threshold period past due for initiation of foreclosure proceedings			120 days
Historical loan loss review period \| Quarter			12
Goodwill and Core Deposit Intangible [Abstract]
Goodwill			$ 65,490	$ 65,490
Finite-lived Intangible Assets [Roll Forward]
Beginning balance, January 1	$ 0	$ 0	133
Ending balance, December 31			$ 0	$ 133
Segment Reporting [Abstract]
Number of operating segments \| Segment			1
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities			$ 25,000
Unrealized holding loss on securities			$ (600)
Federal corporate tax rate			35.00%	35.00%	35.00%
Minimum [Member]
Other Real Estate Owned [Abstract]
Typical frequency of periodic reviews			12 months
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net present value of all potential lease payments			$ 10,100
Maximum [Member]
Other Real Estate Owned [Abstract]
Typical frequency of periodic reviews			18 months
Frequency of periodic reviews in general			24 months
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net present value of all potential lease payments			$ 20,300
Plan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Federal corporate tax rate		21.00%
Buildings [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life			40 years
Furniture, Fixtures, and Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life			2 years
Furniture, Fixtures, and Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life			10 years
Core Deposit Intangible [Member]
Finite-lived Intangible Assets [Roll Forward]
Beginning balance, January 1	0	$ 0	$ 133	$ 291	$ 477
Amortization			(133)	(158)	(186)
Ending balance, December 31			$ 0	$ 133	$ 291
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
ASU 2017-08 [Member] \| Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction in retained earnings	(150)
ASU 2017-08 [Member] \| Forecast [Member] \| Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Quarterly increase in amortization expense	24
ASU 2017-08 [Member] \| Forecast [Member] \| Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Quarterly increase in amortization expense	$ 30