Securities - Fair Value of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 319,746	$ 508,427
Held-to-maturity, Amortized Cost	165,767us-gaap_HeldToMaturitySecurities	9,910us-gaap_HeldToMaturitySecurities
Gross Unrealized Gains	5,697	9,015
Held-to-maturity, Gross Unrealized Gains	4,244
Gross Unrealized Losses	(1,679)	(8,851)
Held-to-maturity, Gross Unrealized Losses	(107)
Available-for-sale Securities, Fair Value	323,764us-gaap_AvailableForSaleSecurities	508,591us-gaap_AvailableForSaleSecurities
Held-to-maturity, Fair Value	169,904	9,910
U.S. Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	26,996	43,808
Held-to-maturity, Amortized Cost	9,804
Gross Unrealized Gains	56	133
Held-to-maturity, Gross Unrealized Gains	82
Gross Unrealized Losses	(229)	(807)
Available-for-sale Securities, Fair Value	26,823	43,134
Held-to-maturity, Fair Value	9,886
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	46,535	176,670
Held-to-maturity, Amortized Cost	129,595	9,910
Gross Unrealized Gains	1,462	4,405
Held-to-maturity, Gross Unrealized Gains	3,398
Gross Unrealized Losses	(45)	(3,177)
Held-to-maturity, Gross Unrealized Losses	(106)
Available-for-sale Securities, Fair Value	47,952	177,898
Held-to-maturity, Fair Value	132,887	9,910
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	122,930	116,047
Held-to-maturity, Amortized Cost	4,039
Gross Unrealized Gains	975	1,242
Held-to-maturity, Gross Unrealized Gains	35
Gross Unrealized Losses	(1,045)	(2,583)
Held-to-maturity, Gross Unrealized Losses	(1)
Available-for-sale Securities, Fair Value	122,860	114,706
Held-to-maturity, Fair Value	4,073
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	122,583	170,006
Held-to-maturity, Amortized Cost	22,329
Gross Unrealized Gains	3,172	3,172
Held-to-maturity, Gross Unrealized Gains	729
Gross Unrealized Losses	(360)	(2,284)
Available-for-sale Securities, Fair Value	125,395	170,894
Held-to-maturity, Fair Value	23,058
Private Labeled Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	670	1,188
Gross Unrealized Gains	19	38
Available-for-sale Securities, Fair Value	689	1,226
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	32	708
Gross Unrealized Gains	13	25
Available-for-sale Securities, Fair Value	$ 45	$ 733

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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