Fair Value of Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair value hierarchy for its financial assets
Transfer of assets between Level 1 to Level 2	$ 0	$ 0
Transfer of liabilities between Level 1 to Level 2	0	0
Transfer of assets between Level 2 to Level 1	0	0
Transfer of liabilities between Level 2 to Level 1	0	0
Fair Value
Fair value hierarchy for its financial assets
Money market funds	1,167	3,012
Total assets	45,230	49,130
Fair Value \| Certificates of deposit
Fair value hierarchy for its financial assets
Available-for-sale securities	5,417	6,429
Fair Value \| Corporate notes
Fair value hierarchy for its financial assets
Available-for-sale securities	19,902	16,719
Fair Value \| U.S. government debt securities
Fair value hierarchy for its financial assets
Available-for-sale securities	18,744	22,970
Level 1
Fair value hierarchy for its financial assets
Money market funds	1,167	3,012
Total assets	1,167	3,012
Level 2
Fair value hierarchy for its financial assets
Total assets	44,063	46,118
Level 2 \| Certificates of deposit
Fair value hierarchy for its financial assets
Available-for-sale securities	5,417	6,429
Level 2 \| Corporate notes
Fair value hierarchy for its financial assets
Available-for-sale securities	19,902	16,719
Level 2 \| U.S. government debt securities
Fair value hierarchy for its financial assets
Available-for-sale securities	$ 18,744	$ 22,970

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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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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-Glossary Cash Equivalents

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