Non-performing Loans and Impaired Loans - Commercial Loans Individually Evaluated for Impairment by Class of Loan (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance total	$ 3,433	$ 5,840	$ 3,433	$ 5,840
Total ending loans balance	3,451	5,855	3,451	5,855
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans total	3,923	6,163	2,642	5,716
Cash/Accrual Interest Income Recognized, Total		1	25	3
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	3,433	5,840	3,433	5,840
Recorded Investment With no recorded allowance	3,451	5,855	3,451	5,855
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	3,923	6,163	2,642	5,716
Cash/Accrual Interest Income Recognized, With no recorded allowance	7	1	25	3
Unpaid Principal Balance With an allowance recorded	0	0	0	0
Recorded Investment With an allowance recorded	0	0	0	0
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans With an allowance recorded	0	0	0	0
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	923	994	923	994
Recorded Investment With no recorded allowance	934	995	934	995
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	1,167	1,029	1,033	1,062
Cash/Accrual Interest Income Recognized, With no recorded allowance	4		4
Unpaid Principal Balance With an allowance recorded	0	0	0	0
Recorded Investment With an allowance recorded	0	0	0	0
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans With an allowance recorded	0	0	0	0
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	701	3,106	701	3,106
Recorded Investment With no recorded allowance	701	3,120	701	3,120
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	468	3,150	308	3,776
Cash/Accrual Interest Income Recognized, With no recorded allowance		1	2	3
Unpaid Principal Balance With an allowance recorded	0	0	0	0
Recorded Investment With an allowance recorded	0	0	0	0
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans With an allowance recorded	0	0	0	0
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Residential Development [Member]
Financing Receivable, Impaired [Line Items]
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Unpaid Principal Balance With an allowance recorded	0	0	0	0
Recorded Investment With an allowance recorded	0	0	0	0
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans With an allowance recorded	0	0	0	0
Cash/Accrual Interest Income Recognized, With an allowance recorded	0	0	0	0
Commercial [Member] \| Development & Spec Land Loans [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance With no recorded allowance	102		102
Recorded Investment With no recorded allowance	102		102
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	222		230
Unpaid Principal Balance With an allowance recorded	0	0	0	0
Recorded Investment With an allowance recorded	0	0	0	0
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans With an allowance recorded	0	0	0	0
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	1,707	1,740	1,707	1,740
Recorded Investment With no recorded allowance	1,714	1,740	1,714	1,740
Allowance For Loan Loss Allocated With no recorded allowance	0	0	0	0
Average Balance in Impaired Loans With no recorded allowance	2,066	1,984	1,071	878
Cash/Accrual Interest Income Recognized, With no recorded allowance	3		19
Unpaid Principal Balance With an allowance recorded	0	0	0	0
Recorded Investment With an allowance recorded	0	0	0	0
Allowance For Loan Loss Allocated	0	0	0	0
Average Balance in Impaired Loans With an allowance recorded	0	0	0	0
Cash/Accrual Interest Income Recognized, With an allowance recorded	$ 0	$ 0	$ 0	$ 0

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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