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Allowance for Loan Losses - Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of the period				$ 16,394				$ 14,837	$ 16,394	$ 14,837	$ 14,534
Total loans charged-off									2,552	2,253	2,660
Total loan recoveries									1,072	1,340	1,121
Net loans charged-off									1,480	913	1,539
Total provision charged to operating expense	$ 528	$ 1,176	$ 635	$ 567	$ 1,100	$ 710	$ 330	$ 330	2,906	2,470	1,842
Balance at the end of the period	$ 17,820				$ 16,394				17,820	16,394	14,837
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									473	629	758
Total loan recoveries									176	298	210
Total provision charged to operating expense									1,699	2,164	(68)
Commercial [Member] \| Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									112	68	181
Total loan recoveries									59	9	31
Commercial [Member] \| Non Owner Occupied Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off										20	471
Total loan recoveries									29	32	55
Commercial [Member] \| Residential Spec Homes [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loan recoveries									8	8	8
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									361	540	106
Total loan recoveries									80	249	116
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									76	89	213
Total loan recoveries									27	44	97
Total provision charged to operating expense									(487)	(81)	(23)
Real Estate [Member] \| Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									76	89	213
Total loan recoveries									27	44	97
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									2,003	1,535	1,689
Total loan recoveries									869	998	814
Total provision charged to operating expense									1,694	387	1,933
Consumer [Member] \| Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									154	137	329
Total loan recoveries									53	501	81
Consumer [Member] \| Indirect Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									1,673	1,193	1,051
Total loan recoveries									505	497	529
Consumer [Member] \| Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans charged-off									176	$ 205	309
Total loan recoveries									$ 311		$ 204