Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less allowance for doubtful accounts	$ (4,114)		$ (4,134)
Accounts Receivable, Net, Current	301,094	$ 284,209	313,451
Contract changes, negotiated settlements and claims for unanticipated contract costs	900		900
Trade receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	164,752		152,078
U.S. Government contracts | Billed | Contract receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	38,173		26,093
U.S. Government contracts | Costs and accrued profit – not billed | Contract receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	780		862
Commercial and other government contracts | Billed | Contract receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	100,603		107,962
Commercial and other government contracts | Costs and accrued profit – not billed | Contract receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 900		$ 30,590