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Marketable Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014
Investments Debt And Equity Securities [Abstract] |  |
Other-than-temporary impairments of investments | $ 0 us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities | $ 0 us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities

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- Definition The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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