Securities - Components of Held to Maturity Securities Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	$ 103,202	$ 110,699
Held to maturity securities, Gross unrecognized gains	2,007	148
Held to maturity securities, Gross unrecognized losses		(1,203)
Held to maturity securities, Fair value	105,209	109,644
Mortgage-Backed GSE Securities: Residential [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	89,642	100,322
Held to maturity securities, Gross unrecognized gains	1,646
Held to maturity securities, Gross unrecognized losses		(1,203)
Held to maturity securities, Fair value	91,288	99,119
States of the U.S. and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to maturity securities, Total amortized cost	13,560	10,377
Held to maturity securities, Gross unrecognized gains	361	148
Held to maturity securities, Fair value	$ 13,921	$ 10,525

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.6)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

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Amount of accumulated unrealized loss on 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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