Revenue (Components of Contracts in Progress) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings in excess of billings for contracts in progress	$ 26,491	$ 31,395
Costs and earnings in excess of billings for completed contracts	10,177	2,823
Total contract revenues in excess of billings	36,668	34,218
Current portion of contract revenues in excess of billings	34,556	32,106
Long-term contract revenues in excess of billings	2,112	2,112
Total billings in excess of contract revenues	(28,833)	(32,608)
Costs And Earnings In Excess Of Billings [Member]
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings for contracts in progress	317,984	199,964
Amounts billed	(291,493)	(168,569)
Billings In Excess Of Costs And Earnings [Member]
Accounts Notes And Loans Receivable [Line Items]
Costs and earnings for contracts in progress	353,952	517,860
Amounts billed	$ (382,785)	$ (550,468)