Loans - Loan Balances by Loan Classification Allocated Between Past Due Performing and Non-performing (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	$ 648,663,000	$ 625,412,000
30 - 89 Days Past Due	1,780,000	393,000
More than 90 days past Due and still Accruing	0	88,000
Non-accrual loans	1,841,000	1,285,000
Special Mention	7,429,000	5,698,000
Substandard	9,164,000	9,495,000
Total loans, gross	668,877,000	642,371,000
Multi-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	30,778,000	37,445,000
Total loans, gross	30,778,000	37,445,000
One-to-Four Family Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	172,824,000	162,724,000
30 - 89 Days Past Due	1,175,000	181,000
More than 90 days past Due and still Accruing		88,000
Non-accrual loans	463,000	266,000
Substandard	559,000	306,000
Total loans, gross	175,021,000	163,565,000
Home Equity Line of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	33,978,000	35,285,000
30 - 89 Days Past Due	13,000
Non-accrual loans	346,000	402,000
Substandard	15,000	10,000
Total loans, gross	34,352,000	35,697,000
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	33,884,000	30,246,000
30 - 89 Days Past Due	152,000
Total loans, gross	34,036,000	30,246,000
Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	10,662,000	14,322,000
Non-accrual loans		40,000
Special Mention	872,000
Substandard		511,000
Total loans, gross	11,534,000	14,873,000
Non-Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	233,277,000	216,692,000
30 - 89 Days Past Due	205,000	209,000
Non-accrual loans	582,000
Special Mention	4,703,000	979,000
Substandard	5,516,000	7,072,000
Total loans, gross	244,283,000	224,952,000
Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	33,016,000	35,253,000
30 - 89 Days Past Due	99,000
Non-accrual loans		111,000
Special Mention	234,000	1,147,000
Substandard		340,000
Total loans, gross	33,349,000	36,851,000
Junior Liens [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	1,127,000	1,180,000
Non-accrual loans	4,000	4,000
Total loans, gross	1,131,000	1,184,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	7,582,000	8,373,000
30 - 89 Days Past Due	39,000	3,000
Non-accrual loans	7,000	3,000
Substandard	317,000	241,000
Total loans, gross	7,945,000	8,620,000
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	91,535,000	83,892,000
30 - 89 Days Past Due	97,000
Non-accrual loans	439,000	459,000
Special Mention	1,620,000	3,572,000
Substandard	2,757,000	1,015,000
Total loans, gross	$ 96,448,000	$ 88,938,000