Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015 security	Dec. 31, 2014 security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions	12	7
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 48,137	$ 59,329
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(171)	(381)
Available-for-sale, Securities, 12 Months or More, Number of Positions	5	13
Available-for-sale Securities, 12 Months or More, Fair Value	39,874	103,527
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(286)	(1,456)
Number of debt securities on which unrealized losses were primarily attributable to changes in interest	17	20
Available-for-sale Securities, Fair Value, Total	88,011	162,856
Available-for-sale Securities, Unrealized Losses, Total	(457)	(1,837)
Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions	3	4
Available-for-sale Securities, Less Than 12 Months, Fair Value	23,523	39,745
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(55)	(207)
Available-for-sale, Securities, 12 Months or More, Number of Positions	4	8
Available-for-sale Securities, 12 Months or More, Fair Value	30,157	63,149
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(148)	(871)
Available-for-sale, Securities, Number of Positions	7	12
Available-for-sale Securities, Fair Value, Total	53,680	102,894
Available-for-sale Securities, Unrealized Losses, Total	(203)	(1,078)
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions	3	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	7,868	9,323
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(25)	(148)
Available-for-sale, Securities, Number of Positions	3	1
Available-for-sale Securities, Fair Value, Total	7,868	9,323
Available-for-sale Securities, Unrealized Losses, Total	(25)	(148)
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions	5
Available-for-sale Securities, Less Than 12 Months, Fair Value	11,361
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(49)
Available-for-sale, Securities, 12 Months or More, Number of Positions		1
Available-for-sale Securities, 12 Months or More, Fair Value		8,982
Available-for-sale Securities, 12 Months or More, Unrealized Losses		(154)
Available-for-sale, Securities, Number of Positions	5	1
Available-for-sale Securities, Fair Value, Total	11,361	8,982
Available-for-sale Securities, Unrealized Losses, Total	(49)	(154)
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions		1
Available-for-sale Securities, Less Than 12 Months, Fair Value		9,998
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses		(25)
Available-for-sale, Securities, 12 Months or More, Number of Positions	1	2
Available-for-sale Securities, 12 Months or More, Fair Value	9,717	20,640
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(138)	(368)
Available-for-sale, Securities, Number of Positions	1	3
Available-for-sale Securities, Fair Value, Total	9,717	30,638
Available-for-sale Securities, Unrealized Losses, Total	(138)	(393)
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions	1	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	5,385	263
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(42)	(1)
Available-for-sale, Securities, 12 Months or More, Number of Positions		2
Available-for-sale Securities, 12 Months or More, Fair Value		10,756
Available-for-sale Securities, 12 Months or More, Unrealized Losses		(63)
Available-for-sale, Securities, Number of Positions	1	3
Available-for-sale Securities, Fair Value, Total	5,385	11,019
Available-for-sale Securities, Unrealized Losses, Total	$ (42)	$ (64)

Number of debt securities on which unrealized losses were primarily attributable to changes in interest.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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