Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	$ 191,633	$ 241,541
Fair value more than 12 months	31,422	11,807
Total fair value	223,055	253,348
Unrealized losses less than 12 months	(4,436)	(8,205)
Unrealized losses more than 12 months	(1,449)	(646)
Total unrealized losses	(5,885)	(8,851)
U.S. Treasury and federal agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	31,303	32,099
Fair value more than 12 months
Total fair value	31,303	32,099
Unrealized losses less than 12 months	(578)	(807)
Unrealized losses more than 12 months
Total unrealized losses	(578)	(807)
State and municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	47,875	57,078
Fair value more than 12 months	5,040	3,206
Total fair value	52,915	60,284
Unrealized losses less than 12 months	(1,578)	(2,993)
Unrealized losses more than 12 months	(250)	(184)
Total unrealized losses	(1,828)	(3,177)
Federal agency collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	42,858	64,445
Fair value more than 12 months	26,382	8,601
Total fair value	69,240	73,046
Unrealized losses less than 12 months	(675)	(2,121)
Unrealized losses more than 12 months	(1,199)	(462)
Total unrealized losses	(1,874)	(2,583)
Federal agency mortgage-backed pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	69,597	87,919
Fair value more than 12 months
Total fair value	69,597	87,919
Unrealized losses less than 12 months	(1,605)	(2,284)
Unrealized losses more than 12 months
Total unrealized losses	$ (1,605)	$ (2,284)