Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	$ 582,321	$ 645,948
Mortgage loans held for sale	4,093	4,392
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	582,321	645,948
Mandatory forward contracts	30,379	20,394
Rate lock loan commitments	27,782	15,639
Mortgage loans held for sale	4,093	4,392
Fair Value, Measurements, Recurring \| U.S. Treasury securities and U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	97,390	152,674
Fair Value, Measurements, Recurring \| Mortgage-backed Securities, Issued by Private Enterprises
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	4,579	4,542
Fair Value, Measurements, Recurring \| Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	254,990	293,329
Fair Value, Measurements, Recurring \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	225,362	195,403
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	577,742
Mortgage loans held for sale	4,093
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	577,742	641,406
Mandatory forward contracts	30,379	20,394
Rate lock loan commitments	27,782	15,639
Mortgage loans held for sale	4,093	4,392
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| U.S. Treasury securities and U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	97,390	152,674
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	254,990	293,329
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring \| Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	225,362	195,403
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	4,579
Fair Value, Inputs, Level 3 \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	4,579	4,542
Fair Value, Inputs, Level 3 \| Fair Value, Measurements, Recurring \| Mortgage-backed Securities, Issued by Private Enterprises
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	$ 4,579	$ 4,542

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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