Securities - Components of Held to Maturity Securities Portfolio (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	$ 113,052,000	$ 0
Held to maturity securities, Gross unrecognized gains	142,000
Held to maturity securities, Gross unrecognized losses	(42,000)
Held to maturity securities, Fair value	113,152,000	$ 0
Mortgage-Backed GSE Securities: Residential [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	103,769,000
Held to maturity securities, Gross unrecognized gains	70,000
Held to maturity securities, Gross unrecognized losses	(36,000)
Held to maturity securities, Fair value	103,803,000
States of the U.S. and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	9,283,000
Held to maturity securities, Gross unrecognized gains	72,000
Held to maturity securities, Gross unrecognized losses	(6,000)
Held to maturity securities, Fair value	$ 9,349,000

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

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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