Allowance for Loan Losses - Internal Risk Rating Grades (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
INTERNAL RISK RATING GRADES
Loan Receivables	$ 854,359	$ 766,296
Pass
INTERNAL RISK RATING GRADES
Loan Receivables	795,879	688,214
Watch
INTERNAL RISK RATING GRADES
Loan Receivables	47,469	64,987
Special Mention
INTERNAL RISK RATING GRADES
Loan Receivables	2,859	1,724
Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	8,147	11,371
Doubtful
INTERNAL RISK RATING GRADES
Loan Receivables	5
Construction, Land and Land Development
INTERNAL RISK RATING GRADES
Loan Receivables	94,750	66,042
Construction, Land and Land Development | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	86,066	55,949
Construction, Land and Land Development | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	6,504	6,690
Construction, Land and Land Development | Special Mention
INTERNAL RISK RATING GRADES
Loan Receivables	127	172
Construction, Land and Land Development | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	2,053	3,231
Farmland
INTERNAL RISK RATING GRADES
Loan Receivables	748	923
Farmland | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	748	923
Commercial Mortgages (Non-Owner Occupied)
INTERNAL RISK RATING GRADES
Loan Receivables	171,996	146,757
Commercial Mortgages (Non-Owner Occupied) | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	166,537	140,625
Commercial Mortgages (Non-Owner Occupied) | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	4,307	5,931
Commercial Mortgages (Non-Owner Occupied) | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	1,152	201
Commercial Mortgages (Owner Occupied)
INTERNAL RISK RATING GRADES
Loan Receivables	82,391	80,052
Commercial Mortgages (Owner Occupied) | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	75,984	67,732
Commercial Mortgages (Owner Occupied) | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	4,712	10,076
Commercial Mortgages (Owner Occupied) | Special Mention
INTERNAL RISK RATING GRADES
Loan Receivables	551
Commercial Mortgages (Owner Occupied) | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	1,144	2,244
Residential First Mortgages
INTERNAL RISK RATING GRADES
Loan Receivables	293,266	269,365
Residential First Mortgages | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	281,677	256,614
Residential First Mortgages | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	7,809	8,624
Residential First Mortgages | Special Mention
INTERNAL RISK RATING GRADES
Loan Receivables	2,048	205
Residential First Mortgages | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	1,732	3,922
Residential Revolving and Junior Mortgages
INTERNAL RISK RATING GRADES
Loan Receivables	39,170	46,498
Residential Revolving and Junior Mortgages | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	37,298	43,659
Residential Revolving and Junior Mortgages | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	1,159	1,376
Residential Revolving and Junior Mortgages | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	713	1,463
Commercial and Industrial
INTERNAL RISK RATING GRADES
Loan Receivables	144,118	114,093
Commercial and Industrial | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	137,964	110,281
Commercial and Industrial | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	4,873	2,373
Commercial and Industrial | Special Mention
INTERNAL RISK RATING GRADES
Loan Receivables		1,347
Commercial and Industrial | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	1,281	92
Consumer
INTERNAL RISK RATING GRADES
Loan Receivables	27,920	42,566
Consumer | Pass
INTERNAL RISK RATING GRADES
Loan Receivables	9,605	12,431
Consumer | Watch
INTERNAL RISK RATING GRADES
Loan Receivables	18,105	29,917
Consumer | Special Mention
INTERNAL RISK RATING GRADES
Loan Receivables	133
Consumer | Substandard
INTERNAL RISK RATING GRADES
Loan Receivables	72	$ 218
Consumer | Doubtful
INTERNAL RISK RATING GRADES
Loan Receivables	$ 5