Loan Portfolio Aging Analysis (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	$ 1,295	$ 1,395
Total Past Due and Non Accrual	2,016	2,679
Current	391,166	365,910
Total Loans Receivable	393,182	368,589
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	387	938
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	275	346
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	59	0
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	19	83
Total Past Due and Non Accrual	19	139
Current	89,825	81,188
Total Loans Receivable	89,844	81,327
Commercial | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	56
Commercial | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	0
Commercial | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	0
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	744	500
Total Past Due and Non Accrual	797	762
Current	214,996	198,174
Total Loans Receivable	215,793	198,936
Commercial Real Estate | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	262
Commercial Real Estate | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	0
Commercial Real Estate | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	53	0
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	513	760
Total Past Due and Non Accrual	1,160	1,625
Current	75,508	74,228
Total Loans Receivable	76,668	75,853
Residential real estate | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	372	559
Residential real estate | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	275	306
Residential real estate | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	0
Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	19	52
Total Past Due and Non Accrual	40	153
Current	10,837	12,320
Total Loans Receivable	10,877	12,473
Installment | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	15	61
Installment | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	0	40
Installment | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non Accrual	$ 6	$ 0