Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Accounting Policies [Abstract]
Impairment of investments	$ 0us-gaap_ImpairmentOfInvestments
Based on these sales prices reduced inventory and increased cost of goods sold	252,000.0	1,100,000
Impairment losses on long lived assets	0us-gaap_AssetImpairmentCharges
Revenue recorded from government contract	141,000us-gaap_ContractsRevenue	125,000us-gaap_ContractsRevenue
Total value of the contract	4,700,000rbcn_GovernmentContractValue
Value of contract recognized	$ 3,400,000
Period of contract	3 years

Government contract period.

No definition available.

Name:	rbcn_GovernmentContractPeriod
Namespace Prefix:	rbcn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Government contract value.

+ References

No definition available.

+ Details

Name:	rbcn_GovernmentContractValue
Namespace Prefix:	rbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Government contract value recorded to date.

+ References

No definition available.

+ Details

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

- Definition

Reduction in inventory and increase in cost of goods sold due to inventory adjustment based on sales prices.

+ References

No definition available.

+ Details

Name:	rbcn_ReductionInInventoryAndIncreaseInCostOfGoodsSoldDueToInventoryAdjustmentBasedOnSalesPrices
Namespace Prefix:	rbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_AccountingPoliciesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228

+ Details

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

- Definition

Revenue earned during the period arising from products sold or services provided under the terms of a contract, not elsewhere specified in the taxonomy. May include government contracts, construction contracts, and any other contract related to a particular project or product.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25351-111560

+ Details

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Balance Type:	debit
Period Type:	duration