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Employee Benefit Plans - Additional Information (Detail) $ in Thousands | 12 Months Ended
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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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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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