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Income Taxes (Details 3) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2014
Operating loss carryforwards |  |  |  |
Reclassification of Unrecognized Tax Benefit Amount |  |  |  | $ 4,700,000 rmbs_ReclassificationofUnrecognizedTaxBenefitAmount
Unrecognized tax benefits, reduction of long-term deferred tax assets, before federal tax benefit | 17,800,000 rmbs_UnrecognizedTaxBenefitsDeferredTaxAssetsNoncurrentGross | 12,600,000 rmbs_UnrecognizedTaxBenefitsDeferredTaxAssetsNoncurrentGross |  |
Unrecognized tax benefits included in long-term income taxes payable | 2,100,000 rmbs_UnrecognizedTaxBenefitsAccruedIncomeTaxesNoncurrent | 6,200,000 rmbs_UnrecognizedTaxBenefitsAccruedIncomeTaxesNoncurrent |  |
Portion of unrecognized tax benefits, which if recognized, would be recorded as an income tax benefit | 2,100,000 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate | 1,600,000 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate |  |
Amount of potential unrecognized tax benefit | 900,000 us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit |  |  |
Reconciliation of the beginning and ending amounts of unrecognized income tax benefits |  |  |  |
Balance at the beginning of the period | 18,794,000 us-gaap_UnrecognizedTaxBenefits | 16,773,000 us-gaap_UnrecognizedTaxBenefits | 16,610,000 us-gaap_UnrecognizedTaxBenefits |
Tax positions related to current year: |  |  |  |
Additions | 1,134,000 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 1,156,000 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 589,000 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions |
Tax positions related to prior years: |  |  |  |
Additions | 531,000 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 956,000 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 1,521,000 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions |
Reductions | (556,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | (91,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | (1,947,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions |
Balance at the end of the period | 19,903,000 us-gaap_UnrecognizedTaxBenefits | 18,794,000 us-gaap_UnrecognizedTaxBenefits | 16,773,000 us-gaap_UnrecognizedTaxBenefits |
Undistributed earnings | 4,200,000 us-gaap_UndistributedEarningsOfForeignSubsidiaries |  |  |
Alternative Minimum Tax Credits |  |  |  |
Operating loss carryforwards |  |  |  |
Tax credit carryforwards | 2,500,000 us-gaap_TaxCreditCarryforwardAmount / us-gaap_TaxCreditCarryforwardAxis = rmbs_AlternativeMinimumTaxCreditsMember |  |  |
Foreign Tax Credit |  |  |  |
Operating loss carryforwards |  |  |  |
Tax credit carryforwards | 120,700,000 us-gaap_TaxCreditCarryforwardAmount / us-gaap_TaxCreditCarryforwardAxis = rmbs_ForeignTaxCreditMember |  |  |
Federal |  |  |  |
Operating loss carryforwards |  |  |  |
Tax credit carryforwards subject to expiration | 55,000,000 rmbs_TaxCreditCarryforwardSubjectToExpirationAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember |  |  |
Federal | Research and Development as label |  |  |  |
Operating loss carryforwards |  |  |  |
Tax credit carryforwards | 32,700,000 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |  |  |
Federal | Excess Tax Benefits From Stock Option Tax Deductions |  |  |  |
Operating loss carryforwards |  |  |  |
Tax credit carryforwards | 36,300,000 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = rmbs_TaxcreditswithnodeferredtaxassetrecognizedMember |  |  |
State |  |  |  |
Operating loss carryforwards |  |  |  |
Operating Loss Carryforwards | 294,500,000 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |  |  |
State | Research and Development as label |  |  |  |
Operating loss carryforwards |  |  |  |
Tax credit carryforwards | 18,600,000 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |  |  |
State | Excess Tax Benefits From Stock Option Tax Deductions |  |  |  |
Operating loss carryforwards |  |  |  |
Operating Loss Carryforwards | $ 97,500,000 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = rmbs_TaxcreditswithnodeferredtaxassetrecognizedMember |  |  |

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