Revenue (Components of Contracts in Progress) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings in excess of billings for contracts in progress	$ 16,137	$ 55,208
Costs and earnings in excess of billings for completed contracts	3,928	22,699
Total contract revenues in excess of billings	20,065	77,907
Contract revenues in excess of billings	17,953	77,907
Long-term contract revenues in excess of billings	2,112
Total billings in excess of contract revenues	(17,793)	(2,586)
Costs And Earnings In Excess Of Billings [Member]
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings for contracts in progress	433,093	507,037
Amounts billed	(416,956)	(451,829)
Costs and earnings for contracts in progress	(433,093)	(507,037)
Billings In Excess Of Costs And Earnings [Member]
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings for contracts in progress	(242,898)	(299,202)
Amounts billed	(260,691)	(301,788)
Costs and earnings for contracts in progress	$ 242,898	$ 299,202