Cash, Cash Equivalents and Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	$ 12,064	$ 17,244	$ 12,064	$ 17,244	$ 12,416	$ 13,245
Available-for-sale securities	70,041		70,041		20,086
Maximum maturity period of U.S. Treasury securities			1 year
Net realized gains or losses	$ 0	$ 0	$ 0	$ 0

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 43

-Section A

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+ Details

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=6506951

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-Name Accounting Standards Codification

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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+ Details