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Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Summary of Significant Accounting Policies (Details)	12 Months Ended
Summary of Significant Accounting Policies (Details)	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