Accounting Policies - Classification of Current Assets and Current Liabilities and Retainage (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Line Items]
Contract liabilities	$ 32,339	$ 51,597	$ 62,700
Billing in excess of cost of earnings, including foreign currency movement, net	$ (19,300)
Retainage collection period upon completion of contract	1 year
Contract receivable retainage due after 12 months percent	10.00%
Minimum
Accounting Policies [Line Items]
Construction period	1 month
Collection period for municipalities	60 days
Retainage, percent of contract value withheld	5.00%
Collection period for other than municipalities	30 days
Maximum
Accounting Policies [Line Items]
Construction period	24 months
Collection period for municipalities	90 days
Retainage, percent of contract value withheld	15.00%
Collection period for other than municipalities	45 days