Loans - Loan Balances by Loan Classification Allocated Between Past Due Performing and Non-performing (Detail) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	$ 658,189,000	$ 625,412,000
30 - 89 Days Past Due	1,605,000	393,000
More than 90 days past Due and still Accruing	0	88,000
Non-accrual loans	1,602,000	1,285,000
Special Mention	6,124,000	5,698,000
Substandard	9,889,000	9,495,000
Total loans, gross	677,409,000	642,371,000
Multi-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	37,742,000	37,445,000
Total loans, gross	37,742,000	37,445,000
One-to-Four Family Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	169,579,000	162,724,000
30 - 89 Days Past Due	884,000	181,000
More than 90 days past Due and still Accruing		88,000
Non-accrual loans	367,000	266,000
Substandard	895,000	306,000
Total loans, gross	171,725,000	163,565,000
Home Equity Line of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	33,875,000	35,285,000
Non-accrual loans	347,000	402,000
Substandard	40,000	10,000
Total loans, gross	34,262,000	35,697,000
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	40,759,000	30,246,000
Total loans, gross	40,759,000	30,246,000
Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	8,535,000	14,322,000
Non-accrual loans		40,000
Substandard	498,000	511,000
Total loans, gross	9,033,000	14,873,000
Non-Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	233,294,000	216,692,000
30 - 89 Days Past Due	366,000	209,000
Non-accrual loans	322,000
Special Mention	5,317,000	979,000
Substandard	5,470,000	7,072,000
Total loans, gross	244,769,000	224,952,000
Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	33,271,000	35,253,000
Non-accrual loans		111,000
Special Mention		1,147,000
Substandard		340,000
Total loans, gross	33,271,000	36,851,000
Junior Liens [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	1,092,000	1,180,000
30 - 89 Days Past Due	13,000
Non-accrual loans	4,000	4,000
Total loans, gross	1,109,000	1,184,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	8,252,000	8,373,000
30 - 89 Days Past Due	15,000	3,000
Non-accrual loans	6,000	3,000
Substandard	252,000	241,000
Total loans, gross	8,525,000	8,620,000
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Currently Performing	91,790,000	83,892,000
30 - 89 Days Past Due	327,000
Non-accrual loans	556,000	459,000
Special Mention	807,000	3,572,000
Substandard	2,734,000	1,015,000
Total loans, gross	$ 96,214,000	$ 88,938,000