Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Additional Information (Detail)

Financial Instruments - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Number of corporate debt securities in an unrealized loss position 23us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1  
Fair value of corporate debt in an unrealized loss position $ 35,800,000us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue  
Available-for-sale securities, gross unrealized loss accumulated in investments 50,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax 9,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Transfer of securities, Level 1 0us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount  
Transfer of securities, Level 2 0us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount  
Transfer of securities, Level 3 $ 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet  
Minimum [Member]    
Debt Instrument [Line Items]    
Due date of company's long term available for sale securities 1 year  
Fair Value Inputs, Discount Rate 0.33%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
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  
Fair Value Inputs, Discount Rate 0.54%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember