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	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 9,065	$ 7,936
Loans Past Due Over 90 Days Still Accruing	162	241
Non-Performing TDRs	1,192	1,014
Performing TDRs	2,015	1,492
Total Non-Performing Loans	12,434	10,683
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	2,921	2,249
Loans Past Due Over 90 Days Still Accruing		183
Non-Performing TDRs	512
Total Non-Performing Loans	3,433	2,432
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	894	1,532
Loans Past Due Over 90 Days Still Accruing		183
Non-Performing TDRs	29
Total Non-Performing Loans	923	1,715
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	218	440
Non-Performing TDRs	483
Total Non-Performing Loans	701	440
Commercial [Member] | Development & Spec Land Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	102	118
Total Non-Performing Loans	102	118
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,707	159
Total Non-Performing Loans	1,707	159
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,269	2,959
Loans Past Due Over 90 Days Still Accruing	119
Non-Performing TDRs	460	809
Performing TDRs	1,697	1,254
Total Non-Performing Loans	5,545	5,022
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,269	2,959
Loans Past Due Over 90 Days Still Accruing	119
Non-Performing TDRs	460	576
Performing TDRs	1,473	1,254
Total Non-Performing Loans	5,321	4,789
Real Estate [Member] | Residential Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Performing TDRs		233
Performing TDRs	224
Total Non-Performing Loans	224	233
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	2,875	2,728
Loans Past Due Over 90 Days Still Accruing	43	58
Non-Performing TDRs	220	205
Performing TDRs	318	238
Total Non-Performing Loans	3,456	3,229
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	310	512
Total Non-Performing Loans	310	512
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,019	659
Loans Past Due Over 90 Days Still Accruing	15	49
Total Non-Performing Loans	1,034	708
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,546	1,557
Loans Past Due Over 90 Days Still Accruing	28	9
Non-Performing TDRs	220	205
Performing TDRs	318	238
Total Non-Performing Loans	$ 2,112	$ 2,009