Fair Value of Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value of Financial Instruments
Corporate debt securities, Amortized Cost	$ 66,406	$ 57,910
Corporate debt securities, Gross Unrealized Gains	15	4
Corporate debt securities, Gross Unrealized Losses	(80)	(158)
Corporate debt securities, Fair Value	66,341us-gaap_AvailableForSaleSecurities	57,756us-gaap_AvailableForSaleSecurities
Contractual maturities of the unrestricted marketable securities held
Less Than 1 Year	39,026
1-5 years	27,315
Corporate debt securities, Fair Value	$ 66,341us-gaap_AvailableForSaleSecurities	$ 57,756us-gaap_AvailableForSaleSecurities

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

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-Name Accounting Standards Codification

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-SubTopic 10

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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