v2.4.1.9

Summary of Significant Accounting Policies Cash and Cash Equivalents (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments	$ 15,000,000us-gaap_ImpairmentOfInvestments	$ 6,700,000us-gaap_ImpairmentOfInvestments	$ 559,000us-gaap_ImpairmentOfInvestments	$ 21,720,000us-gaap_ImpairmentOfInvestments	$ 0us-gaap_ImpairmentOfInvestments
Short-term Investments	200,737,000us-gaap_ShortTermInvestments		275,361,000us-gaap_ShortTermInvestments	200,737,000us-gaap_ShortTermInvestments
Assets, Fair Value Disclosure, Recurring	698,451,000us-gaap_AssetsFairValueDisclosureRecurring		703,928,000us-gaap_AssetsFairValueDisclosureRecurring	698,451,000us-gaap_AssetsFairValueDisclosureRecurring
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	189,500,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue		151,400,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	189,500,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
Cash and Cash Equivalents, at Carrying Value	497,714,000us-gaap_CashAndCashEquivalentsAtCarryingValue		428,567,000us-gaap_CashAndCashEquivalentsAtCarryingValue	497,714,000us-gaap_CashAndCashEquivalentsAtCarryingValue	349,843,000us-gaap_CashAndCashEquivalentsAtCarryingValue	342,211,000us-gaap_CashAndCashEquivalentsAtCarryingValue
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax			132,000us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	(878,000)us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	1,303,000us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
Other Comprehensive Income (Loss), Net of Tax			12,000us-gaap_OtherComprehensiveIncomeLossNetOfTax	(878,000)us-gaap_OtherComprehensiveIncomeLossNetOfTax	1,303,000us-gaap_OtherComprehensiveIncomeLossNetOfTax
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets, Fair Value Disclosure, Recurring	467,120,000us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member		308,666,000us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member	467,120,000us-gaap_AssetsFairValueDisclosureRecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Corporate Bonds and Asset Backed Securities [Domain]
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments	8,563,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_CorporateBondsAndAssetBackedSecuritiesDomain			8,563,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_CorporateBondsAndAssetBackedSecuritiesDomain
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments	160,486,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember		86,877,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember	160,486,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember
Cash and Cash Equivalents, at Carrying Value	31,992,000us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember		120,572,000us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember	31,992,000us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember
Money Market Funds and Demand Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 465,722,000us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_MoneyMarketFundsAndDemandDepositsMember		$ 307,995,000us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_MoneyMarketFundsAndDemandDepositsMember	$ 465,722,000us-gaap_CashAndCashEquivalentsAtCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_MoneyMarketFundsAndDemandDepositsMember

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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