Investment Securities - Gross Unrealized Losses on Investment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 2,631	$ 10,486
Less than 12 months, Unrealized Loss	(16)	(358)
12 months or more, Fair Value	6,956
12 months or more, Unrealized Loss	(96)
Total Fair Value	9,587	10,486
Total Unrealized Loss	(112)	(358)
Less than 12 months, Fair Value, held to maturity	46,861	199,403
Less than 12 months, Unrealized Loss, held to maturity	(156)	(6,995)
12 months or more, Fair Value, held to maturity	63,602
12 months or more, Unrealized Loss, held to maturity	(1,908)
Total Fair Value, held to maturity	110,463	199,403
Total Unrealized Loss, held to maturity	(2,064)	(6,995)
Obligations of U.S. government corporations and agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	2,631	10,287
Less than 12 months, Unrealized Loss	(16)	(357)
12 months or more, Fair Value	6,956
12 months or more, Unrealized Loss	(96)
Total Fair Value	9,587	10,287
Total Unrealized Loss	(112)	(357)
Less than 12 months, Fair Value, held to maturity	46,073	188,218
Less than 12 months, Unrealized Loss, held to maturity	(134)	(5,540)
12 months or more, Fair Value, held to maturity	56,245
12 months or more, Unrealized Loss, held to maturity	(1,796)
Total Fair Value, held to maturity	102,318	188,218
Total Unrealized Loss, held to maturity	(1,930)	(5,540)
Obligations of states and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value		199
Less than 12 months, Unrealized Loss		(1)
Total Fair Value		199
Total Unrealized Loss		(1)
Less than 12 months, Fair Value, held to maturity	788	11,185
Less than 12 months, Unrealized Loss, held to maturity	(22)	(1,455)
12 months or more, Fair Value, held to maturity	7,357
12 months or more, Unrealized Loss, held to maturity	(112)
Total Fair Value, held to maturity	8,145	11,185
Total Unrealized Loss, held to maturity	$ (134)	$ (1,455)