Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	$ 34,286	$ 241,541
Fair value more than 12 months	90,657	11,807
Total fair value	124,941	253,348
Unrealized losses less than 12 months	(225)	(8,205)
Unrealized losses more than 12 months	(1,560)	(646)
Total unrealized losses	(1,786)	(8,851)
U.S. Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	2,993	32,099
Fair value more than 12 months	20,762
Total fair value	23,755	32,099
Unrealized losses less than 12 months	(7)	(807)
Unrealized losses more than 12 months	(222)
Total unrealized losses	(229)	(807)
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	10,287	57,078
Fair value more than 12 months	2,050	3,206
Total fair value	12,336	60,284
Unrealized losses less than 12 months	(121)	(2,993)
Unrealized losses more than 12 months	(30)	(184)
Total unrealized losses	(151)	(3,177)
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	15,013	64,445
Fair value more than 12 months	39,801	8,601
Total fair value	54,813	73,046
Unrealized losses less than 12 months	(88)	(2,121)
Unrealized losses more than 12 months	(957)	(462)
Total unrealized losses	(1,046)	(2,583)
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	5,993	87,919
Fair value more than 12 months	28,044
Total fair value	34,037	87,919
Unrealized losses less than 12 months	(9)	(2,284)
Unrealized losses more than 12 months	(351)
Total unrealized losses	$ (360)	$ (2,284)

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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