Investment Securities - Schedule of Gross Unrealized Losses and Fair Value of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Schedule of Available-for-Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	$ 81,346	$ 156,316	$ 151,072
12 Months or More, Estimated Fair Value	93,467	32,008	8,042
Total Estimated Fair Value	174,813	188,324	159,114
Less Than 12 Months, Unrealized Losses	(514)	(5,396)	(6,641)
12 Months or More, Unrealized Losses	(3,207)	(2,098)	(1,156)
Total Unrealized Losses	(3,721)	(7,494)	(7,797)
US Government Agencies [Member]
Schedule of Available-for-Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value		13,926	13,917
12 Months or More, Estimated Fair Value	14,460
Total Estimated Fair Value	14,460	13,926	13,917
Less Than 12 Months, Unrealized Losses		(1,021)	(1,028)
12 Months or More, Unrealized Losses	(491)
Total Unrealized Losses	(491)	(1,021)	(1,028)
State, County and Municipal Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	10,296	47,401	46,516
12 Months or More, Estimated Fair Value	22,696	3,794	3,807
Total Estimated Fair Value	32,992	51,195	50,323
Less Than 12 Months, Unrealized Losses	(98)	(1,882)	(1,735)
12 Months or More, Unrealized Losses	(616)	(292)	(300)
Total Unrealized Losses	(714)	(2,174)	(2,035)
Corporate Debt Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
12 Months or More, Estimated Fair Value	4,997	4,826	4,235
Total Estimated Fair Value	4,997	4,826	4,235
12 Months or More, Unrealized Losses	(73)	(261)	(856)
Total Unrealized Losses	(73)	(261)	(856)
Mortgage-Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	71,050	94,989	90,639
12 Months or More, Estimated Fair Value	51,314	23,388
Total Estimated Fair Value	122,364	118,377	90,639
Less Than 12 Months, Unrealized Losses	(416)	(2,493)	(3,878)
12 Months or More, Unrealized Losses	(2,027)	(1,545)
Total Unrealized Losses	$ (2,443)	$ (4,038)	$ (3,878)