Balance Sheet Details - Accounts Receivable and Inventory (Details) - USD ($) $ in Millions	Dec. 27, 2015	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 28.5	$ 33.5	$ 54.2	$ 48.4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current accounts receivable	208.6	219.4
Allowance for doubtful accounts	(1.8)	(1.9)
Total accounts receivable, net	206.8	217.5
Retainages receivable	6.4	6.1
Inventory, Net of Allowances, Customer Advances and Progress Billings [Abstract]
Raw materials	32.9	30.1
Work in process	19.2	13.3
Finished goods	2.6	2.8
Supplies and other	1.6	2.1
Subtotal inventoried costs	56.3	48.3
Less customer advances and progress payments	(0.7)	(0.9)
Total inventoried costs	55.6	47.4
Billed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current accounts receivable	96.6	119.0
Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current accounts receivable	112.0	100.4
U.S. Government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total U.S. Government contract receivables	44.5	40.3
U.S. Government | Billed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total U.S. Government contract receivables	13.5	19.1
U.S. Government | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total U.S. Government contract receivables	$ 31.0	$ 21.2