Supplemental Information (Components of Interest Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of components of interest expense
Interest expense, net of capitalized interest	$ 28.1	$ 25.2	$ 18.9
Interest income	1.1	1.6	1.7
Interest expense, net	$ 27.0	$ 23.6	$ 17.2