Fair Value - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Loans held for sale		$ 2,143
Pension plan asset	$ 14,732	15,038	$ 14,553
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	59,724	11,716
Investment securities	28,897	52,690
Loans held for sale		2,143
Loans receivable, net	798,703	642,148
Accrued interest receivable	3,335	2,707
FHLB stock	1,511	964
Pension plan asset	14,735	15,038
Demand deposits	103,001	78,792
Interest-bearing deposits	200,923	195,565
Certificates of deposit	410,061	368,721
Advance payments by borrowers for taxes and insurance	5,025	3,882
Advances	36,400	3,000
Accrued interest payable	42	28
Fair Value Measurements
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	59,724	11,716
Investment securities	28,897	52,690
Loans held for sale		2,143
Loans receivable, net	813,160	660,706
Accrued interest receivable	3,335	2,707
FHLB stock	1,511	964
Pension plan asset	14,696	15,296
Demand deposits	103,001	78,792
Interest-bearing deposits	200,923	195,565
Certificates of deposit	414,902	368,721
Advance payments by borrowers for taxes and insurance	5,025	3,882
Advances	36,400	3,000
Accrued interest payable	42	28
Fair Value Measurements \| Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	59,724	11,716
FHLB stock	1,511	964
Demand deposits	103,001	78,792
Interest-bearing deposits	200,923	195,565
Advances	36,400	3,000
Fair Value Measurements \| Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investment securities	28,897	52,690
Loans held for sale		2,143
Accrued interest receivable	3,335	2,707
Certificates of deposit	414,902	368,721
Advance payments by borrowers for taxes and insurance	5,025	3,882
Accrued interest payable	42	28
Fair Value Measurements \| Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Loans receivable, net	813,160	660,706
Pension plan asset	$ 14,696	$ 15,296

Accrued interest payable fair value.

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Accrued interest receivable fair value.

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Advance payments by borrowers for taxes and insurance fair value.

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Advances from Federal Home Loan Banks and Zions Bank fair value disclosure.

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Certificates of deposit fair value.

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Demand deposit liability fair value.

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Federal home loan bank stock fair value.

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Interest bearing deposit fair value.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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