Allowance for Loan Losses and Impaired Loans (Credit Risk Profile by Internally Assigned Grades) (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	$ 426,103	$ 424,871
Construction and Development
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	26,338	25,475
Farmland
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	33,770	33,353
Residential
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	194,141	199,120
Commercial Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	130,299	125,661
Commercial & agricultural
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	26,731	25,672
Consumer & Other
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	14,824	15,590
Real Estate Secured | Construction and Development
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	26,338	25,475
Real Estate Secured | Farmland
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	33,770	33,353
Real Estate Secured | Residential
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	194,141	199,120
Real Estate Secured | Commercial Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	130,299	125,661
Non-Real Estate Secured | Commercial & agricultural
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	26,731	25,672
Non-Real Estate Secured | Consumer & Other
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	14,824	15,590
Pass
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	377,294	375,900
Pass | Real Estate Secured | Construction and Development
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	25,279	24,612
Pass | Real Estate Secured | Farmland
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	24,548	23,935
Pass | Real Estate Secured | Residential
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	178,153	183,543
Pass | Real Estate Secured | Commercial Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	111,115	106,102
Pass | Non-Real Estate Secured | Commercial & agricultural
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	23,781	22,446
Pass | Non-Real Estate Secured | Consumer & Other
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	14,418	15,262
Watch
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	37,853	35,687
Watch | Real Estate Secured | Construction and Development
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	861	652
Watch | Real Estate Secured | Farmland
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	5,523	4,895
Watch | Real Estate Secured | Residential
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	12,931	12,464
Watch | Real Estate Secured | Commercial Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	15,911	15,291
Watch | Non-Real Estate Secured | Commercial & agricultural
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	2,304	2,057
Watch | Non-Real Estate Secured | Consumer & Other
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	323	328
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	1,408	2,534
Special Mention | Real Estate Secured | Farmland
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	74	74
Special Mention | Real Estate Secured | Residential
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	509	200
Special Mention | Real Estate Secured | Commercial Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	683	1,611
Special Mention | Non-Real Estate Secured | Commercial & agricultural
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	142	649
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	9,548	10,750
Substandard | Real Estate Secured | Construction and Development
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	198	211
Substandard | Real Estate Secured | Farmland
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	3,625	4,449
Substandard | Real Estate Secured | Residential
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	2,548	2,913
Substandard | Real Estate Secured | Commercial Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	2,590	2,657
Substandard | Non-Real Estate Secured | Commercial & agricultural
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	504	$ 520
Substandard | Non-Real Estate Secured | Consumer & Other
Financing Receivable, Recorded Investment [Line Items]
Total of outstanding loans	$ 83