Allowance for Loan Losses - Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of the period	$ 16,394	$ 14,837
Total loans charged-off	716	411
Total loan recoveries	229	298
Net loans charged-off	487	113
Total provision charged to operating expense	567	330
Balance at the end of the period	16,474	15,054
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	13	5
Total loan recoveries	51	135
Total provision charged to operating expense	(1,291)	887
Commercial [Member] | Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	13
Total loan recoveries	12
Commercial [Member] | Non Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loan recoveries	5	22
Commercial [Member] | Residential Spec Homes [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loan recoveries	2	2
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off		5
Total loan recoveries	32	111
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	12	51
Total loan recoveries	6	13
Total provision charged to operating expense	(252)	(567)
Real Estate [Member] | Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	12	51
Total loan recoveries	6	13
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	691	355
Total loan recoveries	172	150
Total provision charged to operating expense	2,110	10
Consumer [Member] | Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	55	20
Total loan recoveries	11	16
Consumer [Member] | Indirect Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	505	285
Total loan recoveries	139	113
Consumer [Member] | Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	131	50
Total loan recoveries	$ 22	$ 21