Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Detail) $ in Thousands	Jun. 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	20	7
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 125,424	$ 59,329
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (1,233)	$ (381)
Available-for-sale, Securities, 12 Months or More, Number of Positions | security	5	13
Available-for-sale Securities, 12 Months or More, Fair Value	$ 39,643	$ 103,527
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (405)	$ (1,456)
Available-for-sale, Securities, Number of Positions | security	25	20
Available-for-sale Securities, Fair Value, Total	$ 165,067	$ 162,856
Available-for-sale Securities, Unrealized Losses, Total	$ (1,638)	$ (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	4	4
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 33,489	$ 39,745
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (215)	$ (207)
Available-for-sale, Securities, 12 Months or More, Number of Positions | security	4	8
Available-for-sale Securities, 12 Months or More, Fair Value	$ 30,033	$ 63,149
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (212)	$ (871)
Available-for-sale, Securities, Number of Positions | security	8	12
Available-for-sale Securities, Fair Value, Total	$ 63,522	$ 102,894
Available-for-sale Securities, Unrealized Losses, Total	$ (427)	$ (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	2	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 17,288	$ 9,323
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (132)	$ (148)
Available-for-sale, Securities, Number of Positions | security	2	1
Available-for-sale Securities, Fair Value, Total	$ 17,288	$ 9,323
Available-for-sale Securities, Unrealized Losses, Total	$ (132)	$ (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	2
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 10,704
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (186)
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	2	1
Available-for-sale Securities, Fair Value, Total	$ 10,704	$ 8,982
Available-for-sale Securities, Unrealized Losses, Total	$ (186)	$ (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	2	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 20,976	$ 9,998
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (180)	$ (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	$ 9,610	$ 20,640
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (193)	$ (368)
Available-for-sale, Securities, Number of Positions | security	3	3
Available-for-sale Securities, Fair Value, Total	$ 30,586	$ 30,638
Available-for-sale Securities, Unrealized Losses, Total	$ (373)	$ (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	10	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 42,967	$ 263
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (520)	$ (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	10	3
Available-for-sale Securities, Fair Value, Total	$ 42,967	$ 11,019
Available-for-sale Securities, Unrealized Losses, Total	$ (520)	$ (64)