Investment Securities - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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)	$ 18,546	$ 16,477
Securities available for sale	778,612	886,560
Amortized Cost	790,082	891,111
Gain (loss) on sales of securities	617	(153)	$ 550
Available-for-sale securities pledged as collateral	445,800	416,100
Held-to-maturity securities pledged as collateral	119,200	$ 45,700
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)

Contractual Maturity Of Securities

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Sales Of Available For Sale 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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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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The fair value of available-for-sale securities that serve as collateral for borrowings.

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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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The carrying amount of held-to-maturity securities that serve as collateral for borrowings.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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