Fair Value of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial Assets:
Securities available for sale	$ 192,287	$ 209,480
Financial liabilities:
Repurchase agreements	117,400	125,600
Amortized Cost [Member]
Financial Assets:
Cash and due from banks	23,469	21,779
Interest-bearing deposits	9,842	3,970
Securities available for sale	192,287	209,480
Federal Home Loan Bank stock	4,428	4,428
Loans held for sale	1,749	1,094
Loans receivable	625,403	604,286
Accrued interest receivable	3,414	3,799
Financial liabilities:
Deposits	731,229	732,882
Advances from borrowers for taxes and insurance	1,188	766
Advances from Federal Home Loan Bank	31,000	11,000
Repurchase agreements	37,829	47,655
Subordinated debentures	10,310	10,310
Estimated Fair Value [Member]
Financial Assets:
Cash and due from banks	23,469	21,779
Interest-bearing deposits	9,842	3,970
Securities available for sale	192,287	209,480
Federal Home Loan Bank stock	4,428	4,428
Loans held for sale	1,749	1,094
Loans receivable	608,134	593,257
Accrued interest receivable	3,414	3,799
Financial liabilities:
Deposits	731,960	732,942
Advances from borrowers for taxes and insurance	1,188	766
Advances from Federal Home Loan Bank	31,069	10,979
Repurchase agreements	37,829	47,655
Subordinated debentures	10,099	10,099
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial Assets:
Cash and due from banks	23,469	21,779
Interest-bearing deposits	9,842	3,970
Securities available for sale		2,001
Significant Other Observable Inputs (Level 2) [Member]
Financial Assets:
Securities available for sale	190,570	205,662
Loans held for sale	1,749	1,094
Financial liabilities:
Deposits	731,960	732,942
Advances from borrowers for taxes and insurance	1,188	766
Advances from Federal Home Loan Bank	31,069	10,979
Repurchase agreements	37,829	47,655
Significant Unobservable Inputs (Level 3) [Member]
Financial Assets:
Securities available for sale	1,717	1,817
Federal Home Loan Bank stock	4,428	4,428
Loans receivable	608,134	593,257
Accrued interest receivable	3,414	3,799
Financial liabilities:
Subordinated debentures	$ 10,099	$ 10,099