(Loss) Income Per Share of Common Stock - Summary of Reconciliation of Numerator and Denominator Used to Calculate Basic and Diluted Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Numerator:
Net (loss) income	$ 7.0	$ (52.0)	$ 12.6	$ 24.3	$ 5.9	$ 18.1	$ (11.1)	$ 5.9	$ 5.1	$ (9.2)	$ 18.0	$ (16.2)
Income allocated to participating securities	(0.2)									0.0	(0.4)	0.0
Net (loss) income for basic EPS	6.8									(9.2)	17.6	(16.2)
Interest on 4 1/16% Debentures	0.3									0.0	0.0	0.0
Net (loss) income for diluted EPS	$ 7.1									$ (9.2)	$ 17.6	$ (16.2)
Denominator:
Basic weighted average shares (in shares)	62.9									73.0	65.6	61.1
Effect of:
4 1/8% Debentures (in shares)	9.4									0.0	0.0	0.0
Employee stock options and stock purchase plan (in shares)	0.2									0.0	0.1	0.0
Diluted weighted average shares (in shares)	72.5									73.0	65.7	61.1
Basic:
Net income (loss) income per share (in USD per share)	$ 0.11					$ 0.26	$ (0.17)	$ 0.09	$ 0.08	$ (0.13)	$ 0.27	$ (0.27)
Diluted:
Net income (loss) per share (in USD per share)	$ 0.10					$ 0.25	$ (0.17)	$ 0.09	$ 0.08	$ (0.13)	$ 0.27	$ (0.27)