Accounts Receivable (Details) - USD ($) $ in Thousands	Apr. 01, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contracts Receivable, Claims and Uncertain Amounts	$ 900	$ 900
Less allowance for doubtful accounts	(2,866)	(2,989)
Accounts receivable, net	252,217	238,102
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	156,480	144,616
U.S. Government [Member] | Billed Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	16,655	20,289
U.S. Government [Member] | Unbilled Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	2,341	4,248
Commercial and Other Government [Member] | Billed Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	72,111	68,066
Commercial and Other Government [Member] | Unbilled Revenues [Member] | Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 7,496	$ 3,872