The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Remaining amortization period 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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Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

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Asset Purchases - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 13, 2013
Business Acquisition [Line Items]
Number of years amortized over an estimated remaining economic useful life of deposits	7 years
Amortization expense	$ 126	$ 203	$ 245
Amortization expense	167
Hicksville [Member]
Business Acquisition [Line Items]
Amortization expense			$ 78
Custar [Member]
Business Acquisition [Line Items]
Amortization expense	$ 167
Custar [Member] \| Core Deposits [Member]
Business Acquisition [Line Items]
Recognition of core deposit intangible asset with acquired purchase				$ 1,170