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Fair Value Measurements (Details) (Recurring basis, Quoted prices in active markets for identical assets (Level 1), USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
U.S. Treasury money market funds
    
Fair Value Measurements    
Investments in U.S. Treasury money market funds and U.S. Treasury securities with maturities less than 90 days $ 34,347us-gaap_CashAndCashEquivalentsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= opht_USTreasuryMoneyMarketFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 $ 35,111us-gaap_CashAndCashEquivalentsFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= opht_USTreasuryMoneyMarketFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
U.S. Treasury securities with maturities less than one year
    
Fair Value Measurements    
Investments in U.S. Treasury securities $ 393,718us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= opht_USTreasurySecuritiesWithMaturitiesLessThanOneYearMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 $ 423,746us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= opht_USTreasurySecuritiesWithMaturitiesLessThanOneYearMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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/ us-gaap_FairValueByMeasurementFrequencyAxis
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