| Financial Instruments - Additional Information (Detail) (USD $) | 3 Months Ended | |
|---|---|---|
| Mar. 31, 2015
 debt_security | Dec. 31, 2014 | |
| Debt Instrument [Line Items] | ||
| Number of corporate debt securities | 22us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 | |
| Fair value of debt | $ 34,000,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue | |
| Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments | 21,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax | 50,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax | 
| Transfer of securities, Level 1 | 0us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount | |
| Transfer of securities, Level 2 | 0us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount | |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net | $ 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet | |
| Minimum [Member] | ||
| Debt Instrument [Line Items] | ||
| Due date of company's long term available for sale securities | 1 year | |
| Maximum [Member] | ||
| Debt Instrument [Line Items] | ||
| Period of unrealized loss position | 12 months | |
| Due date of company's long term available for sale securities | 2 years | 
| X | ||||||||||
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- Definition Available for sale securities noncurrent maturity period. No definition available. 
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| X | ||||||||||
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- Definition Period of unrealized loss position. No definition available. 
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| X | ||||||||||
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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Details 
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| X | ||||||||||
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- Definition Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy. No definition available. 
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| X | ||||||||||
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- Details 
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| X | ||||||||||
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- Details 
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