INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Held to Maturity and Available-for-sale
Held to maturity and available-for-sale securities, Amortized Cost	$ 422,898	$ 401,944
Held to maturity and available-for-sale securities, Gross Unrealized Holding Gains		8
Held to maturity and available-for-sale securities, Gross Unrealized Holding Losses	90	64
Held to maturity and available-for-sale securities, Fair Value	422,808	401,888
Held to maturity and available-for-sale securities, Continuous Unrealized Loss Position less than 12 Months	90	64
Held to Maturity, Available-for-sale, and Trading
Total Fair Value	441,362	434,420
Short-term \| U.S. Treasuries
Held-to-Maturity
Amortized Cost	402	8,034
Gross Unrealized Holding Gains		5
Fair Value	402	8,039
Short-term \| Certificates of deposit
Held-to-Maturity
Amortized Cost	37,594	29,034
Gross Unrealized Holding Gains		1
Fair Value	37,594	29,035
Short-term \| Corporate bonds
Held-to-Maturity
Amortized Cost		2,022
Fair Value		2,022
Short-term \| Municipal securities
Held-to-Maturity
Amortized Cost	330,546	284,605
Gross Unrealized Holding Losses	89	64
Fair Value	330,457	284,541
Continuous Unrealized Loss Position less than 12 Months	89	64
Short-term \| U.S. government agency securities.
Held-to-Maturity
Amortized Cost	19,988	16,005
Gross Unrealized Holding Gains		2
Gross Unrealized Holding Losses	1
Fair Value	19,987	16,007
Continuous Unrealized Loss Position less than 12 Months	1
Short-term \| Variable rate demand notes
Available-for-sale
Amortized Cost	31,058	58,924
Fair Value	31,058	58,924
Short-term \| Auction rate securities
Trading
Fair Value		12,658
Long-term \| Auction rate securities
Available-for-sale
Amortized Cost	3,310	3,320
Fair Value	3,310	3,320
Trading
Fair Value	$ 18,554	$ 19,874

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Represents the cost of debt and equity securities, which are categorized as held-to-maturity and available-for-sale, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Represents the excess of amortized cost basis over the fair value of securities that have been in a loss position for less than twelve months for those securities that are categorized as held-to-maturity and available-for-sale.

+ References

No definition available.

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Represents investments in debt securities which are categorized as held-to-maturity and available-for-sale; such investments are normally measured at amortized cost (carrying value) unless circumstances indicate that the value to be recovered from the investment is less than its carried amount. This element may be used in connection with the fair value disclosures required in footnote disclosures to the financial statements.

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Represents the gross unrealized gains for securities, at a point in time, which are categorized as held-to-maturity and available-for-sale securities.

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No definition available.

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Represents the gross unrealized losses for securities, at a point in time, which are categorized as held-to-maturity and available-for-sale securities.

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No definition available.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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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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This item represents the amortized cost, prior to other than temporary impairment (OTTI), of investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity. The temporary impairments arise from the unrealized losses that are recognized in AOCI.

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This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for those securities which are categorized as held-to-maturity.

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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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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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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 Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

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