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Concentration of Risk and Enterprise Wide Disclosures (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Concentration Risk [Line Items]          
Contract revenues $ 164,017 $ 137,061 $ 433,941 $ 304,607  
Customer concentration risk | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 126,400   $ 126,400   $ 93,398
Concentration risk, percentage     100.00%   100.00%
Customer concentration risk | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 100.00% 100.00% 100.00% 100.00%  
Contract revenues $ 164,017 $ 137,061 $ 433,941 $ 304,607  
Customer concentration risk | Federal Government | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 812   $ 812   $ 4,230
Concentration risk, percentage     1.00%   5.00%
Customer concentration risk | Federal Government | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 8.00% 8.00% 6.00% 11.00%  
Contract revenues $ 13,268 $ 10,629 $ 25,200 $ 34,302  
Customer concentration risk | State Governments | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 6,994   $ 6,994   $ 1,274
Concentration risk, percentage     6.00%   1.00%
Customer concentration risk | State Governments | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 8.00% 6.00% 7.00% 10.00%  
Contract revenues $ 13,285 $ 8,351 $ 29,114 $ 30,924  
Customer concentration risk | Local Governments | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 16,582   $ 16,582   $ 16,650
Concentration risk, percentage     13.00%   18.00%
Customer concentration risk | Local Governments | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 18.00% 32.00% 17.00% 31.00%  
Contract revenues $ 29,718 $ 43,768 $ 71,865 $ 95,076  
Customer concentration risk | Private Companies | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 102,012   $ 102,012   $ 71,244
Concentration risk, percentage     80.00%   76.00%
Customer concentration risk | Private Companies | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 66.00% 54.00% 70.00% 48.00%  
Contract revenues $ 107,746 $ 74,313 $ 307,762 $ 144,305