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, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 15,313	$ 11,548
Loans Past Due Over 90 Days Still Accruing	192	568
Non-Performing TDRs	1,349	1,057
Performing TDRs	2,532	2,002
Total Non-Performing Loans	19,386	15,175
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	8,504	6,094
Loans Past Due Over 90 Days Still Accruing		208
Non-Performing TDRs	793	492
Performing TDRs	453	109
Total Non-Performing Loans	9,750	6,903
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,372	3,413
Non-Performing TDRs	389
Performing TDRs	139	109
Total Non-Performing Loans	3,900	3,522
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,041	554
Non-Performing TDRs	404	492
Performing TDRs	314
Total Non-Performing Loans	3,759	1,046
Commercial [Member] | Development & Spec Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	177	68
Total Non-Performing Loans	177	68
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,653	2,059
Loans Past Due Over 90 Days Still Accruing		208
Total Non-Performing Loans	1,653	2,267
Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	261
Total Non-Performing Loans	261
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,691	2,846
Loans Past Due Over 90 Days Still Accruing	140	180
Non-Performing TDRs	416	423
Performing TDRs	1,748	1,558
Total Non-Performing Loans	5,995	5,007
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,691	2,846
Loans Past Due Over 90 Days Still Accruing	140	180
Non-Performing TDRs	416	423
Performing TDRs	1,748	1,558
Total Non-Performing Loans	5,995	5,007
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	3,118	2,608
Loans Past Due Over 90 Days Still Accruing	52	180
Non-Performing TDRs	140	142
Performing TDRs	331	335
Total Non-Performing Loans	3,641	3,265
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	55	35
Loans Past Due Over 90 Days Still Accruing	17
Total Non-Performing Loans	72	35
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	986	916
Loans Past Due Over 90 Days Still Accruing	30	173
Total Non-Performing Loans	1,016	1,089
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	2,077	1,657
Loans Past Due Over 90 Days Still Accruing	5	7
Non-Performing TDRs	140	142
Performing TDRs	331	335
Total Non-Performing Loans	$ 2,553	$ 2,141