Concentration of Risk and Enterprise Wide Disclosures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended			3 Months Ended					12 Months Ended						3 Months Ended		12 Months Ended			3 Months Ended		12 Months Ended			3 Months Ended		12 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Contract revenues	Dec. 31, 2012 Customer concentration risk Trade and contract retainage receivables	Dec. 31, 2011 Customer concentration risk Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Contract revenues	Sep. 30, 2011 Customer concentration risk Contract revenues	Mar. 31, 2013 Customer concentration risk U.S. Army Corps of Engineers Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk U.S. Army Corps of Engineers Contract revenues	Mar. 31, 2012 Customer concentration risk U.S. Army Corps of Engineers Contract revenues	Dec. 31, 2012 Customer concentration risk Private sector customer Trade and contract retainage receivables	Dec. 31, 2012 Customer concentration risk Private sector customer Contract revenues	Dec. 31, 2012 Customer concentration risk Second Private Sector Customer Trade and contract retainage receivables	Dec. 31, 2012 Customer concentration risk Federal Government Trade and contract retainage receivables	Dec. 31, 2011 Customer concentration risk Federal Government Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Federal Government Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Federal Government Contract revenues	Sep. 30, 2011 Customer concentration risk Federal Government Contract revenues	Dec. 31, 2012 Customer concentration risk State Governments Trade and contract retainage receivables	Dec. 31, 2011 Customer concentration risk State Governments Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk State Governments Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk State Governments Contract revenues	Sep. 30, 2011 Customer concentration risk State Governments Contract revenues	Dec. 31, 2012 Customer concentration risk Local Governments Trade and contract retainage receivables	Dec. 31, 2011 Customer concentration risk Local Governments Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Local Governments Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Local Governments Contract revenues	Sep. 30, 2011 Customer concentration risk Local Governments Contract revenues	Dec. 31, 2012 Customer concentration risk Private Companies Trade and contract retainage receivables	Dec. 31, 2011 Customer concentration risk Private Companies Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Private Companies Trade and contract retainage receivables	Mar. 31, 2013 Customer concentration risk Private Companies Contract revenues	Sep. 30, 2011 Customer concentration risk Private Companies Contract revenues
Concentration Risk [Line Items]
Trade and retainage receivables				$ 53,285		$ 38,327									$ 7,375		$ 11,794			$ 1,761		$ 194			$ 5,532		$ 6,924			$ 38,617		$ 19,415
Concentration risk, percentage				100.00%	100.00%		100.00%	100.00%	16.70%	13.30%	21.00%	14.80%	11.70%	9.90%	31.00%	14.00%		27.00%	25.00%	1.00%	3.00%		8.00%	15.00%	17.00%	10.00%		23.00%	22.00%	51.00%	73.00%		42.00%	38.00%
Contract revenues	$ 75,059	$ 50,890	$ 75,059					$ 50,890										$ 20,031	$ 12,716				$ 6,219	$ 7,520				$ 17,234	$ 11,116				$ 31,575	$ 19,538