Stockholders' Equity - Roll forward of Retained Earnings (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings beginning balance			$ 256.7
Net loss	$ 9.7	$ 0.5	(0.3)	$ (35.5)
Retained earnings ending balance	$ 256.4		$ 256.4

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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