Securities - Maturities of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of debt securities available for sale, due within one year	$ 4,830	$ 4,830
Amortized cost of debt securities available for sale, due in one to five years	26,697	21,564
Amortized cost of debt securities available for sale, due in five to ten years	29,401	41,683
Amortized cost of debt securities available for sale, due after ten years	24,604	33,119
Total amortized cost debt securities available for sale with specific maturities	85,532	101,196
Amortized Cost	234,126	297,848
Estimated fair value of debt securities available for sale, due within one year	4,894	4,927
Estimated fair value of debt securities available for sale, due in one to five years	27,089	21,818
Estimated fair value of debt securities available for sale, due in five to ten years	30,316	42,613
Estimated fair value of debt securities available for sale, due after ten years	26,089	35,380
Total estimated fair value of debt securities available for sale with specific maturities	88,388	104,738
Total unrestricted securities available for sale at estimated fair value	239,922	303,628
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost of debt securities available for sale without specific maturities	84,940	119,347
Total estimated fair value of debt securities available for sale without specific maturities	85,727	119,810
Amortizing Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost of debt securities available for sale without specific maturities	63,654	77,305
Total estimated fair value of debt securities available for sale without specific maturities	$ 65,807	$ 79,080

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of investment in available-for-sale debt securities with a single maturity date.

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Amount of investment in available-for-sale debt securities with a single maturity date at cost, after adjustments, including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in the statement of income and fair value hedge accounting adjustments.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of available-for-sale debt securities at cost, net of adjustments, that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the cost over several maturity groupings. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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