Concentration of Risk and Enterprise-Wide Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018
Concentration Risk [Line Items]
Contract revenues	$ 165,985	$ 159,767	$ 309,090	$ 296,610
Customer concentration risk | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 136,181		$ 136,181			$ 108,375
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	$ 165,985	$ 159,767		$ 309,090	$ 296,610
Customer concentration risk | Federal Government | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 3,420		$ 3,420			$ 2,319
Concentration risk, percentage			3.00%			2.00%
Customer concentration risk | Federal Government | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	8.00%	10.00%		7.00%	10.00%
Contract revenues	$ 12,301	$ 16,077		$ 22,578	$ 29,100
Customer concentration risk | State Governments | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 3,363		$ 3,363			$ 916
Concentration risk, percentage			2.00%			1.00%
Customer concentration risk | State Governments | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	6.00%	6.00%		5.00%	6.00%
Contract revenues	$ 10,286	$ 9,898		$ 14,341	$ 18,274
Customer concentration risk | Local Governments | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 50,017		$ 50,017			$ 30,187
Concentration risk, percentage			37.00%			28.00%
Customer concentration risk | Local Governments | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	31.00%	13.00%		31.00%	15.00%
Contract revenues	$ 51,599	$ 20,522		$ 96,029	$ 43,752
Customer concentration risk | Private Companies | Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 79,381		$ 79,381			$ 74,953
Concentration risk, percentage			58.00%			69.00%
Customer concentration risk | Private Companies | Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	55.00%	71.00%		57.00%	69.00%
Contract revenues	$ 91,799	$ 113,270		$ 176,142	$ 205,484