Revenue (Components of Contracts in Progress) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings in excess of billings for contracts in progress	$ 23,775	$ 16,137
Costs and earnings in excess of billings for completed contracts	9,496	3,928
Total contract revenues in excess of billings	33,271	20,065
Contract revenues in excess of billings	31,159	17,953
Long-term contract revenues in excess of billings	2,112	2,112
Total billings in excess of contract revenues	(50,610)	(17,793)
Costs And Earnings In Excess Of Billings [Member]
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings for contracts in progress	282,443	433,093
Amounts billed	(258,668)	(416,956)
Billings In Excess Of Costs And Earnings [Member]
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings for contracts in progress	465,181	242,898
Amounts billed	$ (515,791)	$ (260,691)