Summary of Significant Accounting Policies (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013 item
Available-for-sale securities
Realized gains (losses) recognized on the sale or maturity of securities	$ 0
Number of securities in unrealized loss position for less than 12 months	18
Aggregate Fair Value	44,992
Unrealized Losses	(23)
Amortized Cost	58,272
Unrealized Gains	3
Unrealized Losses	(23)
Fair Value	58,252
Certificates of deposit
Available-for-sale securities
Amortized Cost	240
Fair Value	240
Commercial paper
Available-for-sale securities
Aggregate Fair Value	9,487
Unrealized Losses	(6)
Amortized Cost	14,487
Unrealized Gains	2
Unrealized Losses	(6)
Fair Value	14,483
Corporate debt securities
Available-for-sale securities
Aggregate Fair Value	35,505
Unrealized Losses	(17)
Amortized Cost	43,545
Unrealized Gains	1
Unrealized Losses	(17)
Fair Value	$ 43,529
Minimum
Available-for-sale securities
Expected average maturities period of marketable securities classified as available-for-sale	3 months
Maximum
Available-for-sale securities
Expected average maturities period of marketable securities classified as available-for-sale	12 months

Represents the expected average maturity period of marketable securities classified as available-for-sale.

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Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities categorized neither as held-to-maturity nor trading securities.

+ References

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

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-Publisher FASB

-Name Emerging Issues Task Force (EITF)

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- Definition

Amount of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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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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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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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.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

-Name Accounting Standards Codification

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

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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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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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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.

+ References

No definition available.

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Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

+ References

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