Fair Value Measurements - Assets and Liabilities on a Recurring Basis (Details) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets
Money market funds	$ 905	$ 10,035
Agency bonds		275
Available-for-sale securities, debt securities	19,301	9,897
TOTAL FINANCIAL ASSETS	20,206	20,207
Level 1 [Member]
Assets
Money market funds	905	10,035
Agency bonds		0
Available-for-sale securities, debt securities	9,013	6,219
TOTAL FINANCIAL ASSETS	9,918	16,254
Level 2 [Member]
Assets
Money market funds	0	0
Agency bonds		275
Available-for-sale securities, debt securities	10,288	3,678
TOTAL FINANCIAL ASSETS	10,288	3,953
Level 3 [Member]
Assets
Money market funds	0	0
Agency bonds		0
Available-for-sale securities, debt securities	0	0
TOTAL FINANCIAL ASSETS	0	0
Obligations of U.S. government agencies [Member]
Assets
Available-for-sale securities, debt securities	9,013	6,219
Obligations of U.S. government agencies [Member] \| Level 1 [Member]
Assets
Available-for-sale securities, debt securities	9,013	6,219
Obligations of U.S. government agencies [Member] \| Level 2 [Member]
Assets
Available-for-sale securities, debt securities	0	0
Obligations of U.S. government agencies [Member] \| Level 3 [Member]
Assets
Available-for-sale securities, debt securities	0	0
Obligations of U.S. corporations [Member]
Assets
Available-for-sale securities, debt securities	6,952	2,630
Obligations of U.S. corporations [Member] \| Level 1 [Member]
Assets
Available-for-sale securities, debt securities	0	0
Obligations of U.S. corporations [Member] \| Level 2 [Member]
Assets
Available-for-sale securities, debt securities	6,952	2,630
Obligations of U.S. corporations [Member] \| Level 3 [Member]
Assets
Available-for-sale securities, debt securities	0	0
Foreign Corporate Debt Securities [Member]
Assets
Available-for-sale securities, debt securities	3,336	1,048
Foreign Corporate Debt Securities [Member] \| Level 1 [Member]
Assets
Available-for-sale securities, debt securities	0	0
Foreign Corporate Debt Securities [Member] \| Level 2 [Member]
Assets
Available-for-sale securities, debt securities	3,336	1,048
Foreign Corporate Debt Securities [Member] \| Level 3 [Member]
Assets
Available-for-sale securities, debt securities	$ 0	$ 0

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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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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- Definition

Debt securities issued by a United States government agency such as Government National Mortgage Association (Ginnie Mae), Federal Home Loan Mortgage Corporation (Freddie Mac), and Federal National Mortgage Association (Fannie Mae), which are 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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