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Background and Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
item
Dec. 31, 2013
Dec. 31, 2012
Background and Significant Accounting Policies      
Number of primary business lines 3exh_NumberOfPrimaryBusinessLines    
Concentrations of Credit Risk      
Minimum period after receivable balances are past due that significant accounts are reviewed individually for collectability 90 days    
Bad debt expenses $ 2.4us-gaap_ProvisionForDoubtfulAccounts $ 2.2us-gaap_ProvisionForDoubtfulAccounts $ 8.8us-gaap_ProvisionForDoubtfulAccounts
Minimum      
Revenue Recognition      
Duration of fabrication projects 3 months    
Maximum      
Revenue Recognition      
Duration of fabrication projects 24 months