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Basis of Presentation (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Nov. 30, 2011
Customer concentration      
Revenues $ 409,995 $ 291,573  
Multiemployer Plans      
Withdrawal liability recorded 7,500   7,500
Revenues | Customer concentration | Top ten customers
     
Customer concentration      
Number of top customers 10 10  
Number of calendar years in which top customers typically generate minimum specified percentage of revenue 1    
Revenues $ 227,000 $ 179,000  
Percentage of concentration risk 55.40% 61.50%  
Revenues | Customer concentration | Top ten customers | Minimum
     
Customer concentration      
Minimum percentage of revenues generated by top ten customers 50.00%    
Revenues | Customer concentration | Large gas and electric utility
     
Customer concentration      
Percentage of concentration risk 8.50% 11.70%  
Revenues | Customer concentration | Large gas pipeline company
     
Customer concentration      
Percentage of concentration risk 7.30%    
Revenues | Customer concentration | One customer
     
Customer concentration      
Percentage of concentration risk 7.30%    
Revenues | Customer concentration | Louisiana DOT
     
Customer concentration      
Percentage of concentration risk   15.20%  
Accounts receivable | Customer concentration | One customer
     
Customer concentration      
Percentage of concentration risk 8.20%