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Summary of Significant Accounting Policies (Details) | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2018 USD ($) segment quarter | Mar. 31, 2019 USD ($) | May 18, 2018 office | Jan. 01, 2018 USD ($) security | Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items] |  |  |  |  |
Number of segments | segment | 3 |  |  |  |
Periods used to calculate general component for allowance for loan losses (in quarters) | quarter | 20 |  |  |  |
Required cash on deposit at Federal Reserve | $ 15,170,000 |  |  |  | $ 10,967,000
ASU 2016-01 |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Number of securities | security |  |  |  | 1 |
ASU 2016-02 | Scenario, Forecast | Subsequent Event |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated increase in total assets as result of new accounting guidance |  | $ 9,300,000 |  |  |
Estimated increase in total liabilities as result of new accounting guidance |  | $ 9,300,000 |  |  |
Branch Acquisition |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Number of branch locations | office |  |  | 5 |  |
River Valley |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Fair value of mortgage servicing rights | $ 995,000 |  |  |  | $ 547,000
Retained Earnings | ASU 2016-01 |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Cumulative effect of new accounting pronouncement in period of adoption |  |  |  | $ 0 |
Accumulated Other Comprehensive Income (Loss) | ASU 2016-01 |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Cumulative effect of new accounting pronouncement in period of adoption |  |  |  | $ 0 |
Minimum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Finite-lived intangible asset, useful life | 6 years |  |  |  |
Maximum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Finite-lived intangible asset, useful life | 10 years |  |  |  |
Buildings and related components | Minimum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Premises, furniture, and equipment, useful life | 10 years |  |  |  |
Buildings and related components | Maximum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Premises, furniture, and equipment, useful life | 40 years |  |  |  |
Furniture, fixtures and equipment | Minimum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Premises, furniture, and equipment, useful life | 3 years |  |  |  |
Furniture, fixtures and equipment | Maximum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Premises, furniture, and equipment, useful life | 10 years |  |  |  |

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