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	$ 15,000,000us-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, within One Year, Fair Value	189,500,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue		151,400,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	189,500,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
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
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments	31,688,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember		151,618,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember	31,688,000us-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			36,866,000us-gaap_ShortTermInvestments / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = idcc_CorporateBondsandAssetBackedSecuritiesMember
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
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

X

- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

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- Definition

Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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X

- Definition

Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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- Definition

Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

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-Section S99

-Paragraph 1

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-Number 210

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