Adjusted quick ratio.

No definition available.

Name:	rbcn_AdjustedQuickRatio
Namespace Prefix:	rbcn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Credit facility.

+ References

No definition available.

+ Details

Name:	rbcn_CreditFacilityTextualAbstract
Namespace Prefix:	rbcn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility basis spread on prime rate.

+ References

No definition available.

+ Details

Name:	rbcn_LineOfCreditFacilityBasisSpreadOnPrimeRate
Namespace Prefix:	rbcn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility maximum borrowing capacity as percentage of accounts receivable.

+ References

No definition available.

+ Details

Name:	rbcn_LineOfCreditFacilityMaximumBorrowingCapacityAsPercentageOfAccountsReceivable
Namespace Prefix:	rbcn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility maximum borrowing capacity as percentage of raw material and finished goods inventory.

+ References

No definition available.

+ Details

Name:	rbcn_LineOfCreditFacilityMaximumBorrowingCapacityAsPercentageOfRawMaterialAndFinishedGoodsInventory
Namespace Prefix:	rbcn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum liquidity amount with lending institution.

+ References

No definition available.

+ Details

Name:	rbcn_MaximumLiquidityAmountWithLendingInstitution
Namespace Prefix:	rbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of cash securities and investments maintained for deposit accounts.

+ References

No definition available.

+ Details

Name:	rbcn_PercentageOfCashSecuritiesAndInvestmentsMaintainedForDepositAccounts
Namespace Prefix:	rbcn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.9)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

Name:	us-gaap_InterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate amount of interest expense on all borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.7,8)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

Name:	us-gaap_InterestExpenseBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage points (also referred to as 'margin') added to the reference rate as stated in the loan agreement and used to compute the variable rate on the loans receivable. For instance, the loan agreement might state that the interest rate the borrower is obligated to pay is the London Interbank Offered Rate (LIBOR) plus three quarters (3/4) of a percentage point adjusted quarterly (each three months). LIBOR in this example is the index or reference rate, 3/4 percentage point is the margin, the reference rate plus the margin is the fully indexed rate. This element would be used to report separately the margin.

+ References

No definition available.

+ Details

Name:	us-gaap_LoansReceivableBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Credit Facility (Details) - USD ($)	1 Months Ended		3 Months Ended		12 Months Ended
Credit Facility (Details) - USD ($)	Aug. 31, 2015	Jan. 31, 2013	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Credit facility (Textual)
Term agreement of senior secured credit facility		3 years
Amount of senior secured credit facility		$ 25,000,000
Percentage of eligible account receivable		80.00%
Percentage of domestically held raw material and finished goods inventory		35.00%
Percentage of advances against inventory	45.00%	40.00%
Amount of aggregate outstanding principal on the revolving line of credit	$ 10,000,000	$ 10,000,000
Option to borrow at an interest rate of LIBOR plus		2.75%
Option to borrow at an interest rate of Wall Street Journal prime rate plus		0.50%
Liquidity rate		$ 20,000,000
Borrowing interest rate options		2.25%
Percentage of unused revolving line facility fee	0.50%	0.375%
Adjusted quick ratio		The Company was required to maintain an adjusted quick ratio of 1.40 to 1.00.
Percentage of maintain operating and other deposit accounts		25.00%
Interest expense				$ 35,000
Interest expense charged on the unused portion of the facility			$ 31,000		$ 92,000