Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of short-term investments
Cost	$ 77,490	$ 77,726
Gross Gains	2
Gross Losses	(361)	(461)
Fair Value	77,131	77,265
Municipal Securities [Member]
Summary of short-term investments
Cost	10,395	11,413
Gross Gains
Gross Losses	(113)	(115)
Fair Value	10,282	11,298
Certificates of Deposits [Member]
Summary of short-term investments
Cost	23,023	23,071
Gross Gains
Fair Value	23,023	23,071
Corporate Debt Securities [Member]
Summary of short-term investments
Cost	30,113	33,723
Gross Gains
Gross Losses	(248)	(327)
Fair Value	29,865	33,396
Commercial Paper [Member]
Summary of short-term investments
Cost	13,959	4,991
Gross Gains	2
Gross Losses		(2)
Fair Value	13,961	4,989
U.S. Agencies [Member]
Summary of short-term investments
Cost		4,528
Gross Gains
Gross Losses		(17)
Fair Value		$ 4,511

Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- 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.

+ References+ Details