Securities - Schedule of Unrealized Losses on Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Unrealized Losses, Total	$ (14,099)	$ (33,861)
Obligations of Government Agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Less than 12 months, Fair Value	18,919	54,356
Less than 12 months, Unrealized Losses	(124)	(1,911)
Less than 12 months, Number of Securities	5	15
12 months or more, Fair Value	19,790	5,083
12 months or more, Unrealized Losses	(520)	(27)
12 months or more, Number of Securities	5	2
Fair Value, Total	38,709	59,439
Unrealized Losses, Total	(644)	(1,938)
Number of Securities Total	10	17
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Less than 12 months, Fair Value	191,506	513,495
Less than 12 months, Unrealized Losses	(1,380)	(14,639)
Less than 12 months, Number of Securities	37	89
12 months or more, Fair Value	239,724	37,002
12 months or more, Unrealized Losses	(8,671)	(2,308)
12 months or more, Number of Securities	42	11
Fair Value, Total	431,230	550,497
Unrealized Losses, Total	(10,051)	(16,947)
Number of Securities Total	79	100
Obligations of State and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Less than 12 months, Fair Value	20,790	181,667
Less than 12 months, Unrealized Losses	(107)	(10,830)
Less than 12 months, Number of Securities	34	277
12 months or more, Fair Value	115,199	47,793
12 months or more, Unrealized Losses	(3,113)	(3,431)
12 months or more, Number of Securities	177	76
Fair Value, Total	135,989	229,460
Unrealized Losses, Total	(3,220)	(14,261)
Number of Securities Total	211	353
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Less than 12 months, Fair Value	4,996	19,837
Less than 12 months, Unrealized Losses	(4)	(560)
Less than 12 months, Number of Securities	1	7
12 months or more, Fair Value	4,525	2,845
12 months or more, Unrealized Losses	(180)	(155)
12 months or more, Number of Securities	2	1
Fair Value, Total	9,521	22,682
Unrealized Losses, Total	(184)	(715)
Number of Securities Total	3	8
Total Temporarily Impaired Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Less than 12 months, Fair Value	236,211	769,355
Less than 12 months, Unrealized Losses	(1,615)	(27,940)
Less than 12 months, Number of Securities	77	388
12 months or more, Fair Value	379,238	92,723
12 months or more, Unrealized Losses	(12,484)	(5,921)
12 months or more, Number of Securities	226	90
Fair Value, Total	615,449	862,078
Unrealized Losses, Total	$ (14,099)	$ (33,861)
Number of Securities Total	303	478