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Business Acquisition - Narrative (Details) (USD $)
 0 Months Ended 12 Months Ended
Oct. 31, 2013
entity
Oct. 31, 2012
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Number of foreign entities the Company acquired ownership interest during period 1orn_BusinessAcquisitionOwnershipAcquiredInForeignEntitiesNumberOfEntities        
Consulting and sales agreement entered into with the acquiree company personnel, contract term   2 years      
Goodwill     33,798,000us-gaap_Goodwill $ 33,798,000us-gaap_Goodwill $ 33,798,000us-gaap_Goodwill
West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Cash paid to acquire business   9,000,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= orn_WestConstructionIncMember		      
Additional potential cash payment consideration, period following acquisition close taken into consideration 12 months        
Contingent consideration, at fair value         271,000us-gaap_BusinessCombinationContingentConsiderationLiability
/ us-gaap_BusinessAcquisitionAxis
= orn_WestConstructionIncMember
Lease agreement with the Seller company, lease term 3 years        
Acquired intangible assets   702,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
/ us-gaap_BusinessAcquisitionAxis
= orn_WestConstructionIncMember		      
Goodwill   2,649,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= orn_WestConstructionIncMember		      
Goodwill acquired during period, amortization period for tax purposes   15 years      
Minimum | West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Acquired intangible assets useful life   1 year      
Maximum | West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Acquired intangible assets useful life   3 years      
Construction equipment | Minimum          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Property and equipment useful life     3 years    
Construction equipment | Minimum | West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Property and equipment useful life   3 years      
Construction equipment | Maximum          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Property and equipment useful life     15 years    
Construction equipment | Maximum | West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Property and equipment useful life   15 years      
Trade name | West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Acquired intangible assets   332,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
/ us-gaap_BusinessAcquisitionAxis
= orn_WestConstructionIncMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TradeNamesMember		      
Acquired intangible assets useful life   1 year      
Backlog | West Construction, Inc.          
Business Combination, Assets and Liabilities Arising from Contingencies [Abstract]          
Acquired intangible assets   370,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
/ us-gaap_BusinessAcquisitionAxis
= orn_WestConstructionIncMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_OrderOrProductionBacklogMember		      
Acquired intangible assets useful life   3 years