Concentration of Risk and Enterprise Wide Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Contract revenues	$ 144,295	$ 164,017	$ 140,301	$ 129,623	$ 161,891	$ 137,061	$ 86,091	$ 81,455	$ 578,236	$ 466,498	$ 385,818
Foreign
Concentration Risk [Line Items]
Contract revenues, percent									1.30%	4.10%	12.90%
Customer concentration risk | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	132,403				107,791				$ 132,403	$ 107,791
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%
Contract revenues									$ 578,236	$ 466,498	$ 385,818
Customer concentration risk | Federal Government | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	5,542				4,230				$ 5,542	$ 4,230
Concentration risk, percentage									4.00%	4.00%
Customer concentration risk | Federal Government | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									7.00%	10.00%	13.00%
Contract revenues									$ 40,361	$ 45,439	$ 47,390
Customer concentration risk | State Governments | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	9,302				1,274				$ 9,302	$ 1,274
Concentration risk, percentage									7.00%	1.00%
Customer concentration risk | State Governments | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									7.00%	9.00%	11.00%
Contract revenues									$ 37,700	$ 42,026	$ 43,147
Customer concentration risk | Local Governments | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	20,886				19,660				$ 20,886	$ 19,660
Concentration risk, percentage									16.00%	18.00%
Customer concentration risk | Local Governments | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									16.00%	28.00%	25.00%
Contract revenues									$ 94,461	$ 130,187	$ 97,145
Customer concentration risk | Private Companies | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 96,673				$ 82,627				$ 96,673	$ 82,627
Concentration risk, percentage									73.00%	77.00%
Customer concentration risk | Private Companies | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									70.00%	53.00%	51.00%
Contract revenues									$ 405,714	$ 248,846	$ 198,136