Supplemental Information (Components of Interest Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of components of interest expense
Interest expense, net of capitalized interest	$ 39.1	$ 32.1	$ 28.1
Interest income	0.8	1.5	1.1
Interest expense, net	$ 38.3	$ 30.6	$ 27.0