Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Detail) (USD $)	Dec. 31, 2014 security	Dec. 31, 2013 security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	7	41
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 59,329,000	$ 274,942,000
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(381,000)	(6,913,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	13	2
Available-for-sale Securities, 12 Months or More, Fair Value	103,527,000	10,088,000
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(1,456,000)	(863,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	20	43
Available-for-sale Securities, Fair Value, Total	162,856,000	285,030,000
Available-for-sale Securities, Unrealized Losses, Total	(1,837,000)	(7,776,000)
Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	4	16
Available-for-sale Securities, Less Than 12 Months, Fair Value	39,745,000	126,017,000
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(207,000)	(2,581,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	8	0
Available-for-sale Securities, 12 Months or More, Fair Value	63,149,000	0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(871,000)	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	12	16
Available-for-sale Securities, Fair Value, Total	102,894,000	126,017,000
Available-for-sale Securities, Unrealized Losses, Total	(1,078,000)	(2,581,000)
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	3
Available-for-sale Securities, Less Than 12 Months, Fair Value	9,323,000	39,522,000
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(148,000)	(603,000)
Available-for-sale Securities, 12 Months or More, Fair Value	0	0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	0	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1	3
Available-for-sale Securities, Fair Value, Total	9,323,000	39,522,000
Available-for-sale Securities, Unrealized Losses, Total	(148,000)	(603,000)
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	0	2
Available-for-sale Securities, Less Than 12 Months, Fair Value	0	22,822,000
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	0	(685,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	1	0
Available-for-sale Securities, 12 Months or More, Fair Value	8,982,000	0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(154,000)	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1	2
Available-for-sale Securities, Fair Value, Total	8,982,000	22,822,000
Available-for-sale Securities, Unrealized Losses, Total	(154,000)	(685,000)
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	4
Available-for-sale Securities, Less Than 12 Months, Fair Value	9,998,000	39,052,000
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(25,000)	(1,305,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	0
Available-for-sale Securities, 12 Months or More, Fair Value	20,640,000	0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(368,000)	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	3	4
Available-for-sale Securities, Fair Value, Total	30,638,000	39,052,000
Available-for-sale Securities, Unrealized Losses, Total	(393,000)	(1,305,000)
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	16
Available-for-sale Securities, Less Than 12 Months, Fair Value	263,000	47,529,000
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	(1,000)	(1,739,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	2
Available-for-sale Securities, 12 Months or More, Fair Value	10,756,000	10,088,000
Available-for-sale Securities, 12 Months or More, Unrealized Losses	(63,000)	(863,000)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	3	18
Available-for-sale Securities, Fair Value, Total	11,019,000	57,617,000
Available-for-sale Securities, Unrealized Losses, Total	(64,000)	(2,602,000)
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized Losses, Total	$ 0