v2.4.1.9
Summary of Significant Accounting Policies Fair Value Measurements (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Concentration Risk, Additional Characteristic three five  
Concentration Risk, Percentage 94.00%us-gaap_ConcentrationRiskPercentage1 96.00%us-gaap_ConcentrationRiskPercentage1  
Assets, Fair Value Disclosure, Recurring $ 703,928,000us-gaap_AssetsFairValueDisclosureRecurring $ 698,451,000us-gaap_AssetsFairValueDisclosureRecurring  
Commercial Paper 120,600,000us-gaap_CommercialPaper 32,000,000us-gaap_CommercialPaper  
Long-term Debt, Excluding Current Maturities 217,835,000us-gaap_LongTermDebtNoncurrent 208,813,000us-gaap_LongTermDebtNoncurrent  
Long-term Debt, Fair Value 255,300,000us-gaap_LongTermDebtFairValue 234,000,000us-gaap_LongTermDebtFairValue  
Investment Owned, at Fair Value     64,300,000us-gaap_IntangibleAssetsGrossExcludingGoodwill
Money Market Funds and Demand Deposits [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 307,995,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
465,722,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
 
Commercial Paper [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 207,449,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
192,478,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
 
US Treasury and Government [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 151,618,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
31,688,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
 
Corporate Bonds and Asset Backed Securities [Domain]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 36,866,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_CorporateBondsAndAssetBackedSecuritiesDomain
   
Corporate Bond Securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring   8,563,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateBondSecuritiesMember
 
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 308,666,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
467,120,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Fair Value, Inputs, Level 1 [Member] | Money Market Funds and Demand Deposits [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 307,995,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
465,722,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Fair Value, Inputs, Level 1 [Member] | Commercial Paper [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Fair Value, Inputs, Level 1 [Member] | Corporate Bonds and Asset Backed Securities [Domain]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 671,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_CorporateBondsAndAssetBackedSecuritiesDomain
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring   1,398,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateBondSecuritiesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 395,262,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
231,331,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Fair Value, Inputs, Level 2 [Member] | Money Market Funds and Demand Deposits [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 207,449,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
192,478,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 151,618,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
31,688,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Fair Value, Inputs, Level 2 [Member] | Corporate Bonds and Asset Backed Securities [Domain]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 36,195,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_CorporateBondsAndAssetBackedSecuritiesDomain
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring   7,165,000us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateBondSecuritiesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Fair Value, Inputs, Level 3 [Member] | Money Market Funds and Demand Deposits [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_MoneyMarketFundsAndDemandDepositsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Fair Value, Inputs, Level 3 [Member] | Commercial Paper [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CommercialPaperMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USTreasuryAndGovernmentMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Fair Value, Inputs, Level 3 [Member] | Corporate Bonds and Asset Backed Securities [Domain]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= idcc_CorporateBondsAndAssetBackedSecuritiesDomain
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Fair Value, Inputs, Level 3 [Member] | Corporate Bond Securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Recurring   $ 0us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateBondSecuritiesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member