Securities - Components of Held to Maturity Securities Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	$ 78,700	$ 82,911
Held to maturity securities, Gross unrecognized gains	19	112
Held to maturity securities, Gross unrecognized losses	(3,907)	(897)
Held to maturity securities, Fair value	74,812	82,126
Mortgage-Backed GSE Securities: Residential [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	66,489	73,682
Held to maturity securities, Gross unrecognized losses	(3,637)	(890)
Held to maturity securities, Fair value	62,852	72,792
States of the U.S. and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	12,211	9,229
Held to maturity securities, Gross unrecognized gains	19	112
Held to maturity securities, Gross unrecognized losses	(270)	(7)
Held to maturity securities, Fair value	$ 11,960	$ 9,334

Amount of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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