Investments and Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of investments
Amortized Cost	$ 68,255	$ 73,262
Gross Unrealized Gains	25	26
Gross Unrealized (Losses)
Estimated Fair Value	68,280	73,288
Cash equivalents [Member]
Schedule of investments
Amortized Cost	10,397	18,836
Gross Unrealized Gains
Estimated Fair Value	10,397	18,836
Available-for-sale securities [Member]
Schedule of investments
Amortized Cost	57,858	54,426
Gross Unrealized Gains	25	26
Gross Unrealized (Losses)
Estimated Fair Value	57,883	54,452
Money market funds [Member] \| Cash equivalents [Member]
Schedule of investments
Amortized Cost	10,397	15,839
Gross Unrealized Gains
Gross Unrealized (Losses)
Estimated Fair Value	10,397	15,839
U.S. government sponsored entity debt securities [Member] \| Cash equivalents [Member]
Schedule of investments
Amortized Cost		2,997
Gross Unrealized Gains
Gross Unrealized (Losses)
Estimated Fair Value		2,997
U.S. government sponsored entity debt securities [Member] \| Available-for-sale securities [Member]
Schedule of investments
Amortized Cost	57,858	54,426
Gross Unrealized Gains	25	26
Gross Unrealized (Losses)
Estimated Fair Value	57,883	54,452
Corporate debt securities [Member] \| Available-for-sale securities [Member]
Schedule of investments
Amortized Cost	0
Gross Unrealized (Losses)
Estimated Fair Value	$ 0

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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