Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Sep. 27, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less allowance for doubtful accounts	$ (3,485)	$ (3,148)
Accounts receivable, net	216,223	180,798
Contract changes, negotiated settlements and claims for unanticipated contract costs	0	397
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	142,805	117,426
U.S. Government [Member] | Billed Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	23,488	18,261
U.S. Government [Member] | Unbilled Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	2,562	2,568
Commercial and Other Government [Member] | Billed Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	50,275	45,547
Commercial and Other Government [Member] | Unbilled Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 578	$ 144