Securities Available-for-Sale - Composition of Securities Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 548,395	$ 510,399
Gross Unrealized Gains	8,344	6,802
Gross Unrealized Losses	(4,843)	(7,776)
Fair Value	551,896	509,425
Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	264,291	235,181
Gross Unrealized Gains	2,109	2,151
Gross Unrealized Losses	(2,216)	(2,581)
Fair Value	264,184	234,751
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	62,114	63,776
Gross Unrealized Gains	693	601
Gross Unrealized Losses	(368)	(603)
Fair Value	62,439	63,774
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	46,519	47,934
Gross Unrealized Gains	1,424	1,420
Gross Unrealized Losses	(391)	(685)
Fair Value	47,552	48,669
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,227	40,357
Gross Unrealized Gains	13	0
Gross Unrealized Losses	(919)	(1,305)
Fair Value	39,321	39,052
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	127,665	115,572
Gross Unrealized Gains	2,481	1,294
Gross Unrealized Losses	(949)	(2,602)
Fair Value	129,197	114,264
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	540,816	502,820
Gross Unrealized Gains	6,720	5,466
Gross Unrealized Losses	(4,843)	(7,776)
Fair Value	542,693	500,510
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,579	7,579
Gross Unrealized Gains	1,624	1,336
Gross Unrealized Losses	0	0
Fair Value	$ 9,203	$ 8,915