Contracts in Progress (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Revenue earned on uncompleted contracts	$ 649,582	$ 557,164
Less: Billings to date	(669,595)	(552,701)
Net underbilling (overbilling)	(20,013)	4,463
Costs and estimated earnings in excess of billing on uncompleted contracts	32,407	33,006
Billings in excess of costs and estimated earnings on uncompleted contracts	(52,420)	(28,543)
Net underbilling (overbilling)	$ (20,013)	$ 4,463