SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2012 objective	Sep. 30, 2011	Dec. 31, 2011
Marketable Securities
Number of objectives of the entity's investment strategy	2
Realized losses		$ 477
Realized gains	4,168
Available-for-sale securities
Amortized Cost	105,820		57,594
Gains in Accumulated Other Comprehensive Income	92
Losses in Accumulated Other Comprehensive Income			(14)
Estimated Fair Value	105,912		57,580
U.S. government agency securities
Available-for-sale securities
Amortized Cost	43,414		28,004
Gains in Accumulated Other Comprehensive Income	33
Losses in Accumulated Other Comprehensive Income			(10)
Estimated Fair Value	43,447		27,994
Corporate bonds
Available-for-sale securities
Amortized Cost	51,630		19,124
Gains in Accumulated Other Comprehensive Income	41
Losses in Accumulated Other Comprehensive Income			(2)
Estimated Fair Value	51,671		19,122
Certificates of deposit
Available-for-sale securities
Amortized Cost	9,179		9,467
Gains in Accumulated Other Comprehensive Income	18
Losses in Accumulated Other Comprehensive Income			(2)
Estimated Fair Value	9,197		9,465
Commercial paper
Available-for-sale securities
Amortized Cost	1,597		999
Estimated Fair Value	$ 1,597		$ 999

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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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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