Other Current Assets (Schedule of Other Current Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid expenses	$ 7.1	$ 6.4
Fair value of derivative assets	0.2	2.2
Other	0.6	2.6
Total other current assets	$ 7.9	$ 11.2