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Credit Facility - Additional Information (Detail) (USD $)
0 Months Ended 3 Months Ended
Jan. 02, 2013
Mar. 31, 2015
Mar. 31, 2014
Jan. 02, 2013
Debt Disclosure [Abstract]        
Term agreement of senior secured credit facility 3 years      
Amount of senior secured credit facility       $ 25,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Percentage of eligible account receivable 80.00%rbcn_LineOfCreditFacilityMaximumBorrowingCapacityAsPercentageOfAccountsReceivable      
Percentage of domestically held raw material and finished goods inventory 35.00%rbcn_LineOfCreditFacilityMaximumBorrowingCapacityAsPercentageOfRawMaterialAndFinishedGoodsInventory      
Percentage of advances against inventory 40.00%rbcn_LineOfCreditFacilityOutstandingMaximumPercentageOfAdvancesAgainstInventory      
Amount of aggregate outstanding principal on the revolving line of credit 10,000,000rbcn_LineOfCreditFacilityOutstandingMaximumAmountOfAdvancesAgainstInventory      
Option to borrow at an interest rate of LIBOR plus 2.75%rbcn_LineOfCreditFacilityBasisSpreadOnLondonInterBankOfferedRate      
Option to borrow at an interest rate of Wall Street Journal prime rate plus 0.50%rbcn_LineOfCreditFacilityBasisSpreadOnPrimeRate      
Liquidity rate 20,000,000rbcn_MaximumLiquidityAmountWithLendingInstitution      
Borrowing interest rate options 2.25%rbcn_LineOfCreditFacilityLiquidityMaintainedBasisSpreadOnLondonInterBankOfferedRate      
Percentage of unused revolving line facility fee 0.375%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage      
Adjusted quick ratio 1.40rbcn_AdjustedQuickRatio      
Percentage of maintain operating and other deposit accounts 25.00%rbcn_PercentageOfCashSecuritiesAndInvestmentsMaintainedForDepositAccounts      
Interest expense charged on the unused portion of the facility   $ 23,000us-gaap_InterestExpense $ 23,000us-gaap_InterestExpense