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Concentration of Risk and Enterprise Wide Disclosures (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Concentration Risk [Line Items]          
Contract revenues $ 137,420 $ 140,301   $ 269,924  
Customer concentration risk | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 120,101   $ 120,101   $ 132,403
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 $ 137,420 $ 140,301 $ 276,177 $ 269,924  
Customer concentration risk | Federal Government | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 5,996   $ 5,996   $ 5,542
Concentration risk, percentage     5.00%   4.00%
Customer concentration risk | Federal Government | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 13.00% 6.00% 14.00% 4.00%  
Contract revenues $ 18,360 $ 7,776 $ 38,092 $ 11,932  
Customer concentration risk | State Governments | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 4,314   $ 4,314   $ 9,302
Concentration risk, percentage     4.00%   7.00%
Customer concentration risk | State Governments | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 9.00% 7.00% 9.00% 6.00%  
Contract revenues $ 12,706 $ 10,462 $ 24,726 $ 15,829  
Customer concentration risk | Local Governments | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 20,183   $ 20,183   $ 20,886
Concentration risk, percentage     17.00%   16.00%
Customer concentration risk | Local Governments | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 15.00% 16.00% 16.00% 16.00%  
Contract revenues $ 20,731 $ 22,470 $ 44,556 $ 42,147  
Customer concentration risk | Private Companies | Trade and contract retainage receivables          
Concentration Risk [Line Items]          
Trade and retainage receivables $ 89,608   $ 89,608   $ 96,673
Concentration risk, percentage     74.00%   73.00%
Customer concentration risk | Private Companies | Contract revenues          
Concentration Risk [Line Items]          
Concentration risk, percentage 63.00% 71.00% 61.00% 74.00%  
Contract revenues $ 85,623 $ 99,593 $ 168,803 $ 200,016