Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	$ 20,879	$ 241,541
Fair value more than 12 months	106,022	11,807
Total fair value	126,901	253,348
Unrealized losses less than 12 months	(82)	(8,205)
Unrealized losses more than 12 months	(2,475)	(646)
Total unrealized losses	(2,557)	(8,851)
U.S. Treasury and federal agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	3,064	32,099
Fair value more than 12 months	23,661
Total fair value	26,725	32,099
Unrealized losses less than 12 months	(20)	(807)
Unrealized losses more than 12 months	(322)
Total unrealized losses	(342)	(807)
State and municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	4,826	57,078
Fair value more than 12 months	4,405	3,206
Total fair value	9,231	60,284
Unrealized losses less than 12 months	(27)	(2,993)
Unrealized losses more than 12 months	(80)	(184)
Total unrealized losses	(107)	(3,177)
Federal agency collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	12,989	64,445
Fair value more than 12 months	42,578	8,601
Total fair value	55,567	73,046
Unrealized losses less than 12 months	(35)	(2,121)
Unrealized losses more than 12 months	(1,386)	(462)
Total unrealized losses	(1,421)	(2,583)
Federal agency mortgage-backed pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months		87,919
Fair value more than 12 months	35,378
Total fair value	35,378	87,919
Unrealized losses less than 12 months		(2,284)
Unrealized losses more than 12 months	(687)
Total unrealized losses	$ (687)	$ (2,284)