Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Sep. 26, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less allowance for doubtful accounts	$ (4,149)	$ (3,827)
Accounts receivable, net	259,035	205,873
Contract changes, negotiated settlements and claims for unanticipated contract costs	0	1,021
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	159,702	125,092
U.S. Government [Member] | Billed Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	14,717	14,364
U.S. Government [Member] | Unbilled Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	4,287	6,340
Commercial and Other Government [Member] | Billed Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	55,472	63,051
Commercial and Other Government [Member] | Unbilled Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 29,006	$ 853