Allowance for Loan Losses - Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of the period	$ 16,474	$ 15,054	$ 16,394	$ 14,837
Total loans charged-off	417	609	1,133	1,020
Total loan recoveries	379	252	608	550
Net loans charged-off	38	357	525	470
Total provision charged to operating expense	635	330	1,202	660
Balance at the end of the period	17,071	15,027	17,071	15,027
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off		255	13	260
Total loan recoveries	40	36	91	171
Total provision charged to operating expense	985	41	(306)	928
Commercial [Member] \| Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off			13
Total loan recoveries		1	12	1
Commercial [Member] \| Non Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loan recoveries	12	3	17	25
Commercial [Member] \| Residential Spec Homes [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loan recoveries	2	2	4	4
Commercial [Member] \| Development & Spec Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off		1		1
Commercial [Member] \| Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off		254		259
Total loan recoveries	26	30	58	141
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	3	1	15	52
Total loan recoveries	5	9	11	22
Total provision charged to operating expense	(117)	93	(369)	(474)
Real Estate [Member] \| Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	3	1	15	52
Total loan recoveries	5	9	11	22
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	414	353	1,105	708
Total loan recoveries	334	207	506	357
Total provision charged to operating expense	(233)	196	1,877	206
Consumer [Member] \| Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	49	9	104	29
Total loan recoveries	21	16	32	32
Consumer [Member] \| Indirect Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off	365	323	870	608
Total loan recoveries	132	152	271	265
Consumer [Member] \| Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off		21	131	71
Total loan recoveries	$ 181	$ 39	$ 203	$ 60

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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