Benefit Plan (Details)	12 Months Ended
Dec. 31, 2018
Benefit Plan
Employee's age limit to participate in the benefit Plan	18 years

Employees eligible age to participate in benefit plan.

No definition available.

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