Non-performing Loans and Impaired Loans - Non-accrual, Loans Past Due Over 90 Days Still on Accrual, and Troubled Debt Restructured ("TDRs") by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 12,062	$ 13,276
Loans Past Due Over 90 Days Still Accruing	30	167
Non-Performing TDRs	1,090	1,013
Performing TDRs	1,899	1,958
Total Non-Performing Loans	15,081	16,414
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	6,330	6,902
Non-Performing TDRs	447	451
Performing TDRs	1	1
Total Non-Performing Loans	6,778	7,354
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	4,921	4,877
Non-Performing TDRs	9	11
Performing TDRs	1	1
Total Non-Performing Loans	4,931	4,889
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	596	115
Non-Performing TDRs	438	440
Total Non-Performing Loans	1,034	555
Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	76	176
Total Non-Performing Loans	76	176
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	737	1,734
Total Non-Performing Loans	737	1,734
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,162	3,693
Non-Performing TDRs	458	351
Performing TDRs	1,656	1,672
Total Non-Performing Loans	5,276	5,716
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,162	3,693
Non-Performing TDRs	458	351
Performing TDRs	1,656	1,450
Total Non-Performing Loans	5,276	5,494
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Performing TDRs		222
Total Non-Performing Loans		222
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	2,570	2,681
Loans Past Due Over 90 Days Still Accruing	30	167
Non-Performing TDRs	185	211
Performing TDRs	242	285
Total Non-Performing Loans	3,027	3,344
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	153	160
Total Non-Performing Loans	153	160
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	866	1,041
Loans Past Due Over 90 Days Still Accruing	30	167
Total Non-Performing Loans	896	1,208
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,551	1,480
Non-Performing TDRs	185	211
Performing TDRs	242	285
Total Non-Performing Loans	$ 1,978	$ 1,976