Investment Securities - Schedule of Amortized Cost and Approximate Fair Value of Investment Securities Classified as Held to Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 21,454	$ 26,408
Gross Unrealized Gains	171	23
Gross Unrealized Losses		(160)
Fair Value	21,625	26,271
Residential mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	7,718	8,373
Gross Unrealized Gains	146	5
Gross Unrealized Losses		(91)
Fair Value	7,864	8,287
Obligations of state and political subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	13,736	14,048
Gross Unrealized Gains	25	18
Gross Unrealized Losses		(5)
Fair Value	$ 13,761	14,061
Obligations of other U.S. government agencies and corporations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		3,987
Gross Unrealized Losses		(64)
Fair Value		$ 3,923

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
-Subparagraph (c)
-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
-SubTopic 210
-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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