Equity Incentive Plan - Summary of Company's Restricted Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	39,970
Expected future remaining compensation expense	$ 408
Expected future compensation expense, restricted shares remaining vesting period	2 years 1 month 2 days
Restricted Shares Awarded on January 15, 2016 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	6,160
Date of Award	Jan. 15, 2016
Expected future remaining compensation expense	$ 41
Expected future compensation expense, restricted shares remaining vesting period	2 years
Restricted Shares Awarded on March 11, 2016 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	5,093
Date of Award	Mar. 11, 2016
Expected future compensation expense, restricted shares remaining vesting period	0 years
Restricted Shares Awarded on March 20, 2017 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	7,632
Date of Award	Mar. 20, 2017
Expected future remaining compensation expense	$ 51
Expected future compensation expense, restricted shares remaining vesting period	1 year
Restricted Shares Awarded on March 20, 2017 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	4,952
Date of Award	Mar. 20, 2017
Expected future remaining compensation expense	$ 77
Expected future compensation expense, restricted shares remaining vesting period	3 years
Restricted Shares Awarded on April 10, 2018 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	7,917
Date of Award	Apr. 10, 2018
Expected future remaining compensation expense	$ 101
Expected future compensation expense, restricted shares remaining vesting period	2 years
Restricted Shares Awarded on April 10, 2018 [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Granted	8,216
Date of Award	Apr. 10, 2018
Expected future remaining compensation expense	$ 138
Expected future compensation expense, restricted shares remaining vesting period	4 years
Restricted Stock [Member]
Schedule Of Nonvested Stock Option Activity [Line Items]
Number of Restricted Shares, Nonvested at beginning of period	42,138	37,050
Number of Restricted Shares, Granted	16,510	17,898
Number of Restricted Shares, Vested	(17,956)	(12,810)
Number of Restricted Shares, Forfeited	(722)	0
Number of Restricted Shares, Nonvested at end of period	39,970	42,138
Weighted Average Grant Date Fair Value, Nonvested at beginning of period	$ 15.60	$ 10.77
Weighted Average Grant Date Fair Value, Granted	22.51	22.15
Weighted Average Grant Date Fair Value, Vested	14.01	10.76
Weighted Average Grant Date Fair Value, Forfeited	19.74	0
Weighted Average Grant Date Fair Value, Nonvested at end of period	$ 19.10	$ 15.60

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Share based compensation arrangement by share based payment award date.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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