Cash, Cash Equivalents and Available for Sale Securities (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Restricted Cash and Cash Equivalents Items [Line Items]
Cash	$ 187,700,000	$ 114,100,000
Investments in cash equivalents	7,900,000	12,200,000
Available for sale securities	88,021,000	120,280,000
Available-for-sale Securities, Current	88,000,000	115,200,000
Available-for-sale Securities, Noncurrent		5,100,000
Available-for-sale Securities, Amortized Cost Basis	87,998,000	120,277,000
Available-for-sale Securities, Fair Value Disclosure	88,021,000	120,280,000
Available-for-sale Securities, Gross Unrealized Gains	23,000	3,000
Restricted cash	5,783,000	5,778,000
Restricted Cash Outstanding Letters of Credit Used For Collateral	5,500,000	5,500,000
Minimum Balance of Letter of Credit	1,000,000
Restricted Cash Guaranteed Investment Certificate for Collateral	300,000	300,000
U.S. government agencies notes [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available for sale securities	21,550,000	55,222,000
Available-for-sale Securities, Amortized Cost Basis	21,539,000	55,222,000
Available-for-sale Securities, Fair Value Disclosure	21,550,000	55,222,000
Available-for-sale Securities, Gross Unrealized Gains	11,000	0
U.S. Treasury notes [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available for sale securities	3,089,000	0
Available-for-sale Securities, Amortized Cost Basis	3,086,000	0
Available-for-sale Securities, Fair Value Disclosure	3,089,000	0
Available-for-sale Securities, Gross Unrealized Gains	3,000	0
Corporate debt securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available for sale securities	63,382,000	65,058,000
Available-for-sale Securities, Amortized Cost Basis	63,373,000	65,055,000
Available-for-sale Securities, Fair Value Disclosure	63,382,000	65,058,000
Available-for-sale Securities, Gross Unrealized Gains	$ 9,000	$ 3,000

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Minimum Balance of Letter of Credit

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Restricted Cash Guaranteed Investment Certificate Used For Collateral

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For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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Investments in debt and equity securities which are categorized neither as trading securities nor held-to-maturity securities and which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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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 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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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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Other (not elsewhere specified in the taxonomy) short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Cash and equivalents whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements.

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