Marketable Securities (Details) (USD $)	9 Months Ended
Sep. 30, 2011 Customer step year statement group source	Dec. 31, 2010
Marketable Securities
Maximum maturity period of available for sale securities (in years)	3
Cash equivalents and marketable securities
Fair Value	$ 264,630,000	$ 494,905,000
Amortized Cost	264,748,000	494,977,000
Gross Unrealized Gains	3,000	37,000
Gross Unrealized Losses	(121,000)	(109,000)
Cash, fair value	28,123,000	17,104,000
Cash	28,123,000	17,104,000
Cash, cash equivalents and marketable securities
Fair Value	292,753,000	512,009,000
Amortized Cost	292,871,000	512,081,000
Gross Unrealized Gains	3,000	37,000
Gross Unrealized Losses	(121,000)	(109,000)
Fair value of Marketable debt securities which have insignificant unrealized losses and will mature within one year	115,400,000
Contractual maturity:
Due within one year	264,630,000	494,905,000
Unrealized Loss, net
Due within one year	(118,000)	(72,000)
Money market funds
Cash equivalents and marketable securities
Fair Value	132,721,000	132,364,000
Amortized Cost	132,721,000	132,364,000
Weighted Rate of Return (as a percent)	0.01%	0.04%
U.S. government sponsored obligations
Cash equivalents and marketable securities
Fair Value	35,668,000	266,817,000
Amortized Cost	35,668,000	266,840,000
Gross Unrealized Gains	3,000	29,000
Gross Unrealized Losses	(3,000)	(52,000)
Weighted Rate of Return (as a percent)	0.25%	0.26%
Corporate notes, bonds and commercial paper
Cash equivalents and marketable securities
Fair Value	96,241,000	95,724,000
Amortized Cost	96,359,000	95,773,000
Gross Unrealized Gains		8,000
Gross Unrealized Losses	(118,000)	(57,000)
Weighted Rate of Return (as a percent)	0.43%	0.39%
Cash equivalents
Cash equivalents and marketable securities
Fair Value	132,721,000	198,158,000
Short term marketable securities
Cash equivalents and marketable securities
Fair Value	$ 131,909,000	$ 296,747,000

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This item represents the weighted rate of return on marketable securities like money market funds, U.S. government bonds and notes, corporate notes, bonds and commercial paper, corporate securities and cash and cash equivalents.

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This item represents the amortized cost of cash, cash equivalents and marketable securities, 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 aggregate of cash, cash equivalents and marketable securities reported on the balance sheet at period end measured at fair value by the entity.

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This item represents the fair value of marketable debt securities which have insignificant unrealized losses and are expected to mature within one year of the balance sheet date.

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Represents the maximum maturity period of securities invested by the entity.

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This item represents unrealized gain (loss) on debt securities which are expected to mature within one year of the balance sheet date and which are categorized neither as held-to-maturity nor as trading securities.

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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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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- 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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-Publisher FASB

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

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Unrestricted cash available for day-to-day operating needs, for an entity that has cash equivalents, but does not aggregate cash equivalents with cash on the balance sheet.

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