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Investment Securities - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Maturity of contract	less than one year
Approximate year of maturity	30 years
Gross Unrealized Gains (Losses)	$ 16,477	$ 24,420
Securities available for sale	886,560	1,309,819
Amortized Cost	891,111	1,317,318
Gain (loss) on sales of securities	(153)	550	$ (1,158)
Available-for-sale securities pledged as collateral	416,100	563,200
Held-to-maturity securities pledged as collateral	45,700
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains (Losses)	500	$ 1,300
Amortized Cost	6,600
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Sale of available securities	75,000
Gain (loss) on sales of securities	$ (300)

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Contractual Maturity Of Securities

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

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Description of how prepayments are considered in determination of contractual cash flows and cash flows expected to be collected for the loan or debt security. This relates to loans and debt securities for which at acquisition it was probable that the investor would be unable to collect all contractually required payments receivable or all cash flows expected at acquisition.

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The net gain (loss) realized from the sale, exchange, redemption, or retirement of securities, not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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