Non-performing Loans and Impaired Loans - Commercial Loans Individually Evaluated for Impairment by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance total	$ 8,634	$ 8,988	$ 8,634	$ 8,988
Total ending loans balance	8,641	8,999	8,641	8,999
Allowance For Loan Loss Allocated	787	184	787	184
Average Balance in Impaired Loans total	11,305	9,720	11,358	9,706
Cash/Accrual Interest Income Recognized, Total	161	71	253	113
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	6,904	8,124	6,904	8,124
Recorded Investment With no recorded allowance	6,911	8,135	6,911	8,135
Average Balance in Impaired Loans With no recorded allowance	9,546	8,849	9,600	8,821
Cash/Accrual Interest Income Recognized, With no recorded allowance	126	71	218	113
Unpaid Principal Balance With an allowance recorded	1,730	864	1,730	864
Recorded Investment With an allowance recorded	1,730	864	1,730	864
Allowance For Loan Loss Allocated	787	184	787	184
Average Balance in Impaired Loans With an allowance recorded	1,759	871	1,758	885
Cash/Accrual Interest Income Recognized, With an allowance recorded	35		35
Commercial [Member] \| Owner Occupied Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	3,851	4,765	3,851	4,765
Recorded Investment With no recorded allowance	3,851	4,762	3,851	4,762
Average Balance in Impaired Loans With no recorded allowance	5,987	5,271	6,005	5,303
Cash/Accrual Interest Income Recognized, With no recorded allowance	76	59	130	96
Unpaid Principal Balance With an allowance recorded	371	864	371	864
Recorded Investment With an allowance recorded	371	864	371	864
Allowance For Loan Loss Allocated	3	184	3	184
Average Balance in Impaired Loans With an allowance recorded	372	871	365	885
Cash/Accrual Interest Income Recognized, With an allowance recorded	10		10
Commercial [Member] \| Non Owner Occupied Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	1,116	1,344	1,116	1,344
Recorded Investment With no recorded allowance	1,143	1,360	1,143	1,360
Average Balance in Impaired Loans With no recorded allowance	1,260	1,591	1,293	1,559
Cash/Accrual Interest Income Recognized, With no recorded allowance	33	5	64	10
Unpaid Principal Balance With an allowance recorded	135		135
Recorded Investment With an allowance recorded	135		135
Allowance For Loan Loss Allocated	40		40
Average Balance in Impaired Loans With an allowance recorded	135		135
Commercial [Member] \| Development & Spec Land [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	140	72	140	72
Recorded Investment With no recorded allowance	139	70	139	70
Average Balance in Impaired Loans With no recorded allowance	226	71	224	73
Cash/Accrual Interest Income Recognized, With no recorded allowance	2		2
Commercial [Member] \| Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	1,797	1,943	1,797	1,943
Recorded Investment With no recorded allowance	1,778	1,943	1,778	1,943
Average Balance in Impaired Loans With no recorded allowance	2,073	1,916	2,078	1,886
Cash/Accrual Interest Income Recognized, With no recorded allowance	15	$ 7	22	$ 7
Unpaid Principal Balance With an allowance recorded	1,224		1,224
Recorded Investment With an allowance recorded	1,224		1,224
Allowance For Loan Loss Allocated	744		744
Average Balance in Impaired Loans With an allowance recorded	1,252		1,258
Cash/Accrual Interest Income Recognized, With an allowance recorded	$ 25		$ 25

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