Inventories - Long term contracts percentage-of-completion accounting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jul. 01, 2016	Jun. 30, 2017	Jul. 01, 2016
Inventory Disclosure [Abstract]
Increase to operating income from the quarterly impact of revisions in long term contracts	$ 1.1		$ 2.1
Decrease to operating income from the quarterly impact of revisions in long term contracts		$ 1.6		$ 2.6