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INCOME TAXES (Tax Credit Carryforwards and Income Tax Uncertainties) (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Tax Credit Carryforward [Line Items]        
Unrecognized tax benefits $ 3,252,000us-gaap_UnrecognizedTaxBenefits $ 2,397,000us-gaap_UnrecognizedTaxBenefits $ 836,000us-gaap_UnrecognizedTaxBenefits $ 937,000us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits that would impact effective tax rate 2,700,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate      
Federal | Research Tax Credit Carryforward        
Tax Credit Carryforward [Line Items]        
Tax credit carryforwards 7,900,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_ResearchMember		      
State | Research Tax Credit Carryforward        
Tax Credit Carryforward [Line Items]        
Tax credit carryforwards 8,300,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_ResearchMember		      
State | Research Tax Credit Carryforward | Stock Option Deductions In Excess Of Book Expense        
Tax Credit Carryforward [Line Items]        
Tax credit carryforwards 3,900,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_ResearchMember
/ rkus_TaxCreditCarryforwardNatureOfTransactionAxis
= rkus_StockOptionDeductionsInExcessOfBookExpenseMember		      
Foreign        
Tax Credit Carryforward [Line Items]        
Tax credit carryforwards $ 500,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_ForeignCountryMember