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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Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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- Definition

Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an 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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Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets
Investments	$ 72,238
Liabilities
Convertible preferred stock warrants (in shares)		1,516
Corporate debt securities
Assets
Investments	59,533
Certificate of deposit
Assets
Investments	240
Commercial paper
Assets
Investments	12,465
Recurring basis \| Level 1
Assets
Cash equivalents - money market funds	25,668
Recurring basis \| Level 1 \| U.S. treasury securities
Assets
Cash equivalents		35,076
Recurring basis \| Level 2 \| Corporate debt securities
Assets
Cash equivalents	5,017
Investments	59,533
Recurring basis \| Level 2 \| Certificate of deposit
Assets
Cash equivalents	480
Investments	240
Recurring basis \| Level 2 \| Commercial paper
Assets
Investments	12,465
Recurring basis \| Level 3
Liabilities
Convertible preferred stock warrants (in shares)		1,516
Derivative liability	$ 196