Securities (Detail) - Securities Portfolio (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Securities Available-for-Sale
Amortized Cost	$ 1,192,322
Fair Value	1,187,009us-gaap_AvailableForSaleSecurities	1,112,725us-gaap_AvailableForSaleSecurities
Securities Held-to-Maturity
Municipal securities, at amortized cost	26,555us-gaap_HeldToMaturitySecurities	44,322us-gaap_HeldToMaturitySecurities
Municipal securities, Unrealized Holding Gains	1,115	0
Municipal securities, Unrecognized Holding Losses	0	(935)
Municipal securities, Fair Value	27,670	43,387
Trading Securities	17,460us-gaap_TradingSecurities	17,317us-gaap_TradingSecurities
U.S. Agency Securities
Securities Available-for-Sale
Amortized Cost	30,297	500
Gross Unrealized Gains	144	0
Gross Unrealized Losses	(10)	0
Fair Value	30,431	500
Collateralized Mortgage Obligations
Securities Available-for-Sale
Amortized Cost	538,882	490,962
Gross Unrealized Gains	2,256	1,427
Gross Unrealized Losses	(6,982)	(16,621)
Fair Value	534,156	475,768
Other Mortgage Backed Securities
Securities Available-for-Sale
Amortized Cost	155,443	135,097
Gross Unrealized Gains	4,632	3,349
Gross Unrealized Losses	(310)	(2,282)
Fair Value	159,765	136,164
Municipal Securities
Securities Available-for-Sale
Amortized Cost	414,255	457,318
Gross Unrealized Gains	10,583	9,673
Gross Unrealized Losses	(1,018)	(5,598)
Fair Value	423,820	461,393
Trust-preferred Collateralized Debt Obligations
Securities Available-for-Sale
Amortized Cost	48,502	46,532
Gross Unrealized Gains	152	0
Gross Unrealized Losses	(14,880)	(28,223)
Fair Value	33,774	18,309
Corporate Debt Securities
Securities Available-for-Sale
Amortized Cost	1,719	12,999
Gross Unrealized Gains	83	1,930
Gross Unrealized Losses	0	0
Fair Value	1,802	14,929
Equity Securities
Securities Available-for-Sale
Amortized Cost	3,224	3,706
Gross Unrealized Gains	72	2,046
Gross Unrealized Losses	(35)	(90)
Fair Value	3,261	5,662
Total
Securities Available-for-Sale
Amortized Cost	1,192,322	1,147,114
Gross Unrealized Gains	17,922	18,425
Gross Unrealized Losses	(23,235)	(52,814)
Fair Value	$ 1,187,009	$ 1,112,725

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

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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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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