Concentration of Risk and Enterprise Wide Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Concentration Risk [Line Items]
Contract revenues	$ 161,891	$ 137,061	$ 86,091	$ 81,455	$ 107,333	$ 106,976	$ 90,251	$ 81,258	$ 466,498	$ 385,818	$ 354,544
Foreign
Concentration Risk [Line Items]
Contract revenues, percent									4.10%	12.90%	8.50%
Customer concentration risk | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	107,791				52,788				$ 107,791	$ 52,788
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									$ 466,498	$ 385,818	$ 354,544
Customer concentration risk | Private sector customer | Trade and contract retainage receivables
Concentration Risk [Line Items]
Concentration risk, percentage										14.00%
Customer concentration risk | US Army Corps of Engineers | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage											11.70%
Customer concentration risk | Federal Government | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	4,230				4,607				$ 4,230	$ 4,607
Concentration risk, percentage									4.00%	9.00%
Customer concentration risk | Federal Government | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									10.00%	13.00%	19.00%
Contract revenues									$ 45,439	$ 47,390	$ 65,926
Customer concentration risk | State Governments | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	1,274				476				$ 1,274	$ 476
Concentration risk, percentage									1.00%	1.00%
Customer concentration risk | State Governments | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									9.00%	11.00%	9.00%
Contract revenues									$ 42,026	$ 43,147	$ 30,451
Customer concentration risk | Local Governments | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	19,660				13,927				$ 19,660	$ 13,927
Concentration risk, percentage									18.00%	26.00%
Customer concentration risk | Local Governments | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									28.00%	25.00%	15.00%
Contract revenues									$ 130,187	$ 97,145	$ 54,702
Customer concentration risk | Private Companies | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 82,627				$ 33,778				$ 82,627	$ 33,778
Concentration risk, percentage									77.00%	64.00%
Customer concentration risk | Private Companies | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage									53.00%	51.00%	57.00%
Contract revenues									$ 248,846	$ 198,136	$ 203,465