Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Detail) $ in Thousands	Sep. 30, 2015 USD ($) security	Dec. 31, 2014 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions | security	4	7
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 29,737	$ 59,329
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (144)	$ (381)
Available-for-sale, Securities, 12 Months or More, Number of Positions | security	3	13
Available-for-sale Securities, 12 Months or More, Fair Value	$ 24,429	$ 103,527
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (70)	$ (1,456)
Available-for-sale, Securities, Number of Positions | security	7	20
Available-for-sale Securities, Fair Value, Total	$ 54,166	$ 162,856
Available-for-sale Securities, Unrealized Losses, Total	$ (214)	$ (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 | security	0	4
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 39,745
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ (207)
Available-for-sale, Securities, 12 Months or More, Number of Positions | security	2	8
Available-for-sale Securities, 12 Months or More, Fair Value	$ 14,720	$ 63,149
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (28)	$ (871)
Available-for-sale, Securities, Number of Positions | security	2	12
Available-for-sale Securities, Fair Value, Total	$ 14,720	$ 102,894
Available-for-sale Securities, Unrealized Losses, Total	$ (28)	$ (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 | security	1	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 10,694	$ 9,323
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (11)	$ (148)
Available-for-sale, Securities, Number of Positions | security	1	1
Available-for-sale Securities, Fair Value, Total	$ 10,694	$ 9,323
Available-for-sale Securities, Unrealized Losses, Total	$ (11)	$ (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 | security	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 8,377
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (80)
Available-for-sale, Securities, 12 Months or More, Number of Positions | security		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 | security	1	1
Available-for-sale Securities, Fair Value, Total	$ 8,377	$ 8,982
Available-for-sale Securities, Unrealized Losses, Total	$ (80)	$ (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 | security		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 | security	1	2
Available-for-sale Securities, 12 Months or More, Fair Value	$ 9,709	$ 20,640
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (42)	$ (368)
Available-for-sale, Securities, Number of Positions | security	1	3
Available-for-sale Securities, Fair Value, Total	$ 9,709	$ 30,638
Available-for-sale Securities, Unrealized Losses, Total	$ (42)	$ (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 | security	2	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 10,666	$ 263
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (53)	$ (1)
Available-for-sale, Securities, 12 Months or More, Number of Positions | security		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 | security	2	3
Available-for-sale Securities, Fair Value, Total	$ 10,666	$ 11,019
Available-for-sale Securities, Unrealized Losses, Total	$ (53)	$ (64)