Investments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 56,170	$ 76,606
Gross Gains	44
Gross Losses		(257)
Fair Value	56,214	76,349
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	28,855	26,575
Gross Gains	25
Gross Losses		(139)
Fair Value	28,880	26,436
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	14,931	18,464
Gross Gains	4
Gross Losses		(2)
Fair Value	14,935	18,462
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	12,384	12,520
Gross Gains	15
Gross Losses		(116)
Fair Value	12,399	12,404
Certificates of Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		19,047
Gross Gains
Fair Value		$ 19,047

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

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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