Allowance for Loan Losses - Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of the period	$ 17,071	$ 15,027	$ 16,394	$ 14,837
Total loans charged-off	671	663	1,804	1,683
Total loan recoveries	222	512	830	1,062
Net loans charged-off	449	151	974	621
Total provision charged to operating expense	1,176	710	2,378	1,370
Balance at the end of the period	17,798	15,586	17,798	15,586
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	206	264	219	524
Total loan recoveries	27	106	118	277
Total provision charged to operating expense	1,895	429	1,589	1,357
Commercial [Member] \| Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	97	12	110	12
Total loan recoveries	7	7	19	8
Commercial [Member] \| Non Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off		20		20
Total loan recoveries	5	4	22	29
Commercial [Member] \| Residential Spec Homes [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loan recoveries	2	2	6	6
Commercial [Member] \| Development & Spec Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off				1
Commercial [Member] \| Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	109	232	109	491
Total loan recoveries	13	93	71	234
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	2	37	17	89
Total loan recoveries	4	13	15	35
Total provision charged to operating expense	(243)	361	(612)	(113)
Real Estate [Member] \| Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	2	37	17	89
Total loan recoveries	4	13	15	35
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	463	362	1,568	1,070
Total loan recoveries	191	393	697	750
Total provision charged to operating expense	(476)	(80)	1,401	126
Consumer [Member] \| Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	20	84	124	113
Total loan recoveries	10	249	42	281
Consumer [Member] \| Indirect Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	432	254	1,302	862
Total loan recoveries	107	119	378	384
Consumer [Member] \| Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	11	24	142	95
Total loan recoveries	$ 74	$ 25	$ 277	$ 85

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount, after recoveries, of loans and leases that have been written-off.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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