Amortized Cost and Approximate Fair Values, Together with Gross Unrealized Gains and Losses of Securities (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Amortized Cost	$ 30,587
Available-for-sale Securities, Gross Unrealized Gains	61
Available-for-sale Securities, Gross Unrealized Losses	(2)
Available-for-sale securities, Fair Value	30,646	$ 19,348
Held-to-maturity Securities, Amortized Cost	235	450
Held-to-maturity Securities, Gross Unrealized Gains		127
Held-to-maturity Securities, Gross Unrealized Losses		(67)
Held-to-maturity Securities, Fair Value	236	19,348
U.S. government agencies
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Amortized Cost	27,000	14,443
Available-for-sale Securities, Gross Unrealized Gains	25	4
Available-for-sale Securities, Gross Unrealized Losses	(2)	(67)
Available-for-sale securities, Fair Value	27,023	14,380
State and political subdivisions
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Amortized Cost	3,587	4,841
Available-for-sale Securities, Gross Unrealized Gains	36	105
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale securities, Fair Value	3,623	4,946
Held-to-maturity Securities, Amortized Cost	235	450
Held-to-maturity Securities, Gross Unrealized Gains	1	1
Held-to-maturity Securities, Gross Unrealized Losses	0	0
Held-to-maturity Securities, Fair Value	$ 236	451
Equity securities
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Amortized Cost		4
Available-for-sale Securities, Gross Unrealized Gains		18
Available-for-sale Securities, Gross Unrealized Losses		0
Available-for-sale securities, Fair Value		$ 22

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of unrecognized gain before loss on investments in held-to-maturity securities.

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Amount of unrecognized loss before gain on investments in held-to-maturity securities. Excludes write-down for other than temporary impairment (OTTI).

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