Supplemental Information (Components of Interest Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of components of interest expense
Interest expense, net of capitalized interest	$ 25.2	$ 18.9	$ 16.5
Interest income	1.6	1.7	2.0
Interest expense, net	$ 23.6	$ 17.2	$ 14.5