Securities - Maturities of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of debt securities available for sale, due within one year	$ 0	$ 0
Amortized cost of debt securities available for sale, due in one to five years	21,013	17,939
Amortized cost of debt securities available for sale, due in five to ten years	42,557	42,151
Amortized cost of debt securities available for sale, due after ten years	16,294	22,702
Total amortized cost debt securities available for sale with specific maturities	79,864	82,792
Amortized Cost	231,618	233,429
Estimated fair value of debt securities available for sale, due within one year	0	0
Estimated fair value of debt securities available for sale, due in one to five years	21,525	18,304
Estimated fair value of debt securities available for sale, due in five to ten years	43,739	42,793
Estimated fair value of debt securities available for sale, due after ten years	17,671	24,088
Total estimated fair value of debt securities available for sale with specific maturities	82,935	85,185
Total unrestricted securities available for sale at estimated fair value	237,829	237,177
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost of debt securities available for sale without specific maturities	94,155	89,690
Total estimated fair value of debt securities available for sale without specific maturities	94,994	89,543
Amortizing Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost of debt securities available for sale without specific maturities	57,599	60,947
Total estimated fair value of debt securities available for sale without specific maturities	$ 59,900	$ 62,449

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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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through 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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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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