v2.4.1.9

Summary of Significant Accounting Policies Short-Term Investments (Details) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2013 | Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Other than Temporary Impairment Losses, Investments | $ 15,000,000 us-gaap_ImpairmentOfInvestments | $ 6,700,000 us-gaap_ImpairmentOfInvestments | $ 559,000 us-gaap_ImpairmentOfInvestments | $ 21,720,000 us-gaap_ImpairmentOfInvestments | $ 0 us-gaap_ImpairmentOfInvestments
Short-term Investments | 200,737,000 us-gaap_ShortTermInvestments |  | 275,361,000 us-gaap_ShortTermInvestments | 200,737,000 us-gaap_ShortTermInvestments |
Assets, Fair Value Disclosure, Recurring | 698,451,000 us-gaap_AssetsFairValueDisclosureRecurring |  | 703,928,000 us-gaap_AssetsFairValueDisclosureRecurring | 698,451,000 us-gaap_AssetsFairValueDisclosureRecurring |
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value | 189,500,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue |  | 151,400,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue | 189,500,000 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue |
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax |  |  | 132,000 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax | (878,000)us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax | 1,303,000 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
US Treasury and Government [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Short-term Investments | 31,688,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |  | 151,618,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember | 31,688,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
Corporate Bonds and Asset Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Short-term Investments |  |  | 36,866,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_CorporateBondsandAssetBackedSecuritiesMember |  |
Commercial Paper [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Short-term Investments | 160,486,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember |  | 86,877,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember | 160,486,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember |
Corporate Bonds and Asset Backed Securities [Domain] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Short-term Investments | $ 8,563,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_CorporateBondsAndAssetBackedSecuritiesDomain |  |  | $ 8,563,000 us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_CorporateBondsAndAssetBackedSecuritiesDomain |

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