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Employee Benefits - Narrative (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
401 (k) Retirement Plan [Abstract]      
Minimum service period for plan eligibility 6 months    
Minimum allowable contribution to the plan by each employee, percent 1.00%orn_DefinedContributionPlanAnnualContributionByEmployeeMinimumAllowableAmountPercent    
Maximum allowable contribution to the plan by each employee, percent 80.00%orn_DefinedContributionPlanAnnualContributionByEmployeeMaximumAllowableAmountPercent    
Employers matching contribution, vesting period 4 years    
Company contributions to the plan $ 1.2us-gaap_DefinedContributionPlanCostRecognized $ 1.0us-gaap_DefinedContributionPlanCostRecognized $ 1.0us-gaap_DefinedContributionPlanCostRecognized
Range 1      
401 (k) Retirement Plan [Abstract]      
Employer matching contribution, percent 100.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
/ orn_ContributionPlanEmployerMatchingContributionAxis
= orn_RangeOneMember
   
Employer matching contribution, percent of employee's gross pay 2.00%orn_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployeesGrossPay
/ orn_ContributionPlanEmployerMatchingContributionAxis
= orn_RangeOneMember
   
Range 2      
401 (k) Retirement Plan [Abstract]      
Employer matching contribution, percent 50.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
/ orn_ContributionPlanEmployerMatchingContributionAxis
= orn_RangeTwoMember
   
Employer matching contribution, percent of employee's gross pay 2.00%orn_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployeesGrossPay
/ orn_ContributionPlanEmployerMatchingContributionAxis
= orn_RangeTwoMember