Non-performing Loans and Impaired Loans - Commercial Loans Individually Evaluated for Impairment by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance total	$ 8,194	$ 8,355	$ 8,194	$ 8,355
Total ending loans balance	8,198	8,358	8,198	8,358
Allowance For Loan Loss Allocated	906	924	906	924
Average Balance in Impaired Loans total	11,021	9,228	11,141	9,311
Cash/Accrual Interest Income Recognized, Total	197	(17)	425	96
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	6,161	6,573	6,161	6,573
Recorded Investment With no recorded allowance	6,165	6,576	6,165	6,576
Average Balance in Impaired Loans With no recorded allowance	8,957	7,437	9,052	7,509
Cash/Accrual Interest Income Recognized, With no recorded allowance	163	(25)	360	88
Unpaid Principal Balance With an allowance recorded	2,033	1,782	2,033	1,782
Recorded Investment With an allowance recorded	2,033	1,782	2,033	1,782
Allowance For Loan Loss Allocated	906	924	906	924
Average Balance in Impaired Loans With an allowance recorded	2,064	1,791	2,089	1,802
Cash/Accrual Interest Income Recognized, With an allowance recorded	34	8	65	8
Commercial [Member] \| Owner Occupied Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	3,718	4,496	3,718	4,496
Recorded Investment With no recorded allowance	3,719	4,490	3,719	4,490
Average Balance in Impaired Loans With no recorded allowance	5,854	5,014	5,895	5,077
Cash/Accrual Interest Income Recognized, With no recorded allowance	83	(25)	259	71
Unpaid Principal Balance With an allowance recorded	370	845	370	845
Recorded Investment With an allowance recorded	370	845	370	845
Allowance For Loan Loss Allocated	3	145	3	145
Average Balance in Impaired Loans With an allowance recorded	371	852	367	874
Cash/Accrual Interest Income Recognized, With an allowance recorded	4		14
Commercial [Member] \| Non Owner Occupied Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	427	841	427	841
Recorded Investment With no recorded allowance	427	857	427	857
Average Balance in Impaired Loans With no recorded allowance	459	936	504	1,119
Cash/Accrual Interest Income Recognized, With no recorded allowance	8	(5)	15	5
Unpaid Principal Balance With an allowance recorded	126	187	126	187
Recorded Investment With an allowance recorded	126	187	126	187
Allowance For Loan Loss Allocated	35	30	35	30
Average Balance in Impaired Loans With an allowance recorded	130	189	133	178
Cash/Accrual Interest Income Recognized, With an allowance recorded		4		4
Commercial [Member] \| Development & Spec Land [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	140	71	140	71
Recorded Investment With no recorded allowance	140	69	140	69
Average Balance in Impaired Loans With no recorded allowance	225	69	224	72
Cash/Accrual Interest Income Recognized, With no recorded allowance	1		3
Commercial [Member] \| Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	1,876	1,165	1,876	1,165
Recorded Investment With no recorded allowance	1,879	1,160	1,879	1,160
Average Balance in Impaired Loans With no recorded allowance	2,419	1,418	2,429	1,241
Cash/Accrual Interest Income Recognized, With no recorded allowance	71	5	83	12
Unpaid Principal Balance With an allowance recorded	1,537	750	1,537	750
Recorded Investment With an allowance recorded	1,537	750	1,537	750
Allowance For Loan Loss Allocated	868	749	868	749
Average Balance in Impaired Loans With an allowance recorded	1,563	750	1,589	750
Cash/Accrual Interest Income Recognized, With an allowance recorded	$ 30	$ 4	$ 51	$ 4

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