Supplemental Information - Prepaid and Other Current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Income and value added tax receivables	$ 8.2	$ 10.7
Prepaid freight and supply agreements	0.8	0.8
Prepaid insurance	1.3	1.5
Non-trade receivables	2.4	5.6
Advances to suppliers	0.8	0.8
Equity securities (Note 5)	1.8	0.0
Other	5.5	4.3
Prepaid and other current assets	$ 20.8	$ 23.7