Investments and Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of available-for-sale securities
Amortized Cost	$ 77,272	$ 82,612
Gross Unrealized Gains		19
Gross unrealized (losses)	(7)	(7)
Estimated Fair Value	77,265	82,624
Cash equivalents [Member]
Schedule of available-for-sale securities
Amortized Cost	15,021	15,258
Gross Unrealized Gains
Gross unrealized (losses)
Estimated Fair Value	15,021	15,258
Marketable securities [Member]
Schedule of available-for-sale securities
Amortized Cost	62,251	67,354
Gross Unrealized Gains		19
Gross unrealized (losses)	(7)	(7)
Estimated Fair Value	62,244	67,366
Money market funds [Member] \| Cash equivalents [Member]
Schedule of available-for-sale securities
Amortized Cost	15,021	15,258
Gross Unrealized Gains
Gross unrealized (losses)
Estimated Fair Value	15,021	15,258
U.S. government sponsored entity debt securities [Member] \| Marketable securities [Member]
Schedule of available-for-sale securities
Amortized Cost	47,865	27,020
Gross Unrealized Gains
Gross unrealized (losses)	(5)	(7)
Estimated Fair Value	47,860	27,013
U.S. treasury debt securities [Member] \| Marketable securities [Member]
Schedule of available-for-sale securities
Amortized Cost		751
Gross Unrealized Gains		1
Estimated Fair Value		752
Corporate debt securities [Member] \| Marketable securities [Member]
Schedule of available-for-sale securities
Amortized Cost	14,386	39,583
Gross Unrealized Gains		18
Gross unrealized (losses)	(2)
Estimated Fair Value	$ 14,384	$ 39,601

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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