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Employee Benefit Plans - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Employee shares	Dec. 31, 2017 USD ($) Employee shares	Dec. 31, 2016 USD ($) Employee shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Minimum percentage of eligible compensation on a pre-tax basis for eligible employees to save	1.00%
Employee contribution matching percentage	50.00%
Percentage of total eligible compensation, contribution by Bank, maximum limit	4.00%
Vesting percentage in participant's deferral contributions and employer matching contributions	100.00%
Vesting period	6 years
Employer matching contribution and the discretionary contribution | $	$ 1,100	$ 972	$ 877
Restricted stock awards, shares issued	33,000	32,000	32,300
Awards grants originated in 2013, 2014 and 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees, received the stock | Employee			4
Four employees received shares from awards granted due to retirement			2,394
Awards grants originated in 2014, 2015 and 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees, received the stock | Employee		1
One employee received shares from awards granted due to retirement		640
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Stock issued to number of employees | Employee	80	74	74
Shares vest under the plan	100.00%	100.00%	100.00%
Shares forfeited due to employee termination	2,620	1,080	1,546
Number of shares vested	28,790	24,870	22,444
Number of employees, received the stock | Employee	56	52	45
Compensation expense | $	$ 745	$ 507	$ 402
One employee received shares from awards granted due to retirement		640	2,394
Unrecognized compensation cost related to the nonvested portion of restricted stock awards under the plan | $	$ 1,900
Restricted Stock Awards [Member] | 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested			20,050
Restricted Stock Awards [Member] | 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested		24,230
Restricted Stock Awards [Member] | 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested	28,790

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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