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Basis of Presentation (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Nov. 30, 2011
Customer concentration          
Revenues $ 445,013 $ 337,436 $ 855,008 $ 629,009  
Multiemployer Plans          
Withdrawal liability recorded 7,500   7,500   7,500
Revenues | Customer concentration | Top ten customers
         
Customer concentration          
Number of top customers 10 10 10 10  
Number of calendar years in which top customers typically generate minimum specified percentage of revenue     1    
Revenues $ 216,000 $ 185,000 $ 443,000 $ 364,000  
Percentage of concentration risk 48.60% 54.80% 51.90% 57.90%  
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 7.60% 12.10% 8.00% 11.90%  
Revenues | Customer concentration | Large gas pipeline company
         
Customer concentration          
Percentage of concentration risk 8.20%   5.00%    
Revenues | Customer concentration | One customer
         
Customer concentration          
Percentage of concentration risk     6.40% 4.10%  
Revenues | Customer concentration | Louisiana DOT
         
Customer concentration          
Percentage of concentration risk   11.60%   13.30%  
Accounts receivable | Customer concentration | One customer
         
Customer concentration          
Percentage of concentration risk     6.50% 6.80%