Amortized Cost and Estimated Fair Value of Held-to-Maturity Securities, Including Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 816	$ 816
Unrealized Gains	8	16
Unrealized Losses
Fair Value	824	832
Municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	816	816
Unrealized Gains	8	16
Unrealized Losses
Fair Value	$ 824	$ 832

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

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As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

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- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

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