Inventoried Costs (Details) - USD ($) $ in Millions	Jun. 25, 2017	Dec. 25, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 31.4	$ 31.9
Work in process	29.3	22.1
Finished goods	2.0	1.4
Supplies and other	2.0	1.8
Subtotal inventoried costs	64.7	57.2
Less: Customer advances and progress payments	(3.2)	(1.8)
Total inventoried costs	$ 61.5	$ 55.4