Accounts Receivable, Net - Schedule of Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Jun. 29, 2018	Jan. 01, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less allowance for doubtful accounts	$ (4,063)		$ (4,134)
Accounts receivable, net	250,293	$ 284,209	313,451
Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	165,835		152,078
U.S. Government contracts | Billed | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	19,355		26,093
U.S. Government contracts | Not billed | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	1,230		862
Commercial and other government contracts | Billed | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	67,025		107,962
Commercial and other government contracts | Not billed | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 911		$ 30,590