Non-performing Loans and Impaired Loans - Commercial Loans Individually Evaluated for Impairment by Class of Loan (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance total	$ 8,988	$ 3,639	$ 8,988	$ 3,639
Total ending loans balance	8,999	3,640	8,999	3,640
Allowance For Loan Loss Allocated	184		184
Average Balance in Impaired Loans total	9,720	3,262	9,706	2,518
Cash/Accrual Interest Income Recognized, Total	71	40	113	40
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	8,124	3,639	8,124	3,639
Recorded Investment With no recorded allowance	8,135	3,640	8,135	3,640
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	8,849	3,262	8,821	2,518
Cash/Accrual Interest Income Recognized, With no recorded allowance	71	40	113	40
Unpaid Principal Balance With an allowance recorded	864		864
Recorded Investment With an allowance recorded	864		864
Allowance For Loan Loss Allocated	184		184
Average Balance in Impaired Loans With an allowance recorded	871		885
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Owner Occupied Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	4,765	1,591	4,765	1,591
Recorded Investment With no recorded allowance	4,762	1,592	4,762	1,592
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	5,271	1,538	5,303	1,233
Cash/Accrual Interest Income Recognized, With no recorded allowance	59	22	96	22
Unpaid Principal Balance With an allowance recorded	864		864
Recorded Investment With an allowance recorded	864		864
Allowance For Loan Loss Allocated	184		184
Average Balance in Impaired Loans With an allowance recorded	871		885
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Non Owner Occupied Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	1,344	467	1,344	467
Recorded Investment With no recorded allowance	1,360	467	1,360	467
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	1,591	471	1,559	432
Cash/Accrual Interest Income Recognized, With no recorded allowance	5	2	10	2
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Residential Spec Homes [Member]
Financing Receivable, Impaired [Line Items]
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Development & Spec Land [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	72	107	72	107
Recorded Investment With no recorded allowance	70	107	70	107
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	71	230	73	234
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	1,943	1,474	1,943	1,474
Recorded Investment With no recorded allowance	1,943	1,474	1,943	1,474
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	1,916	1,023	1,886	619
Cash/Accrual Interest Income Recognized, With no recorded allowance	7	16	7	16
Cash/Accrual Interest Income Recognized, With an allowance recorded	$ 0	$ 0	$ 0	$ 0

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