Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) years	Jan. 01, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Management's estimate of total cost of ultimate disposition of known environmental matters | $	$ 9.4	$ 9.9
Number of years over which estimated environmental cost will be paid | years	10