Basic and Diluted Income Per Common Share - Basic Income (Loss) Per Common Share to Diluted Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net (loss) income attributable to common stock and participating preferred stockholders	$ (31.5)	$ 155.6
Participating shares at end of period:
Weighted-average Common stock outstanding (in shares)	44.8	44.3
Unvested restricted stock (in shares)	0.6	0.4
Preferred stock (as-converted basis) (in shares)	2.1	4.9
Total (in shares)	47.5	49.6
Percentage of loss allocated to:
Common stock	94.30%	89.30%
Unvested restricted stock	1.30%	0.80%
Preferred stock	4.40%	9.90%
Net (loss) income attributable to common stock, basic	$ (29.7)	$ 139.0
Distributed and Undistributed earnings to Common Shareholders:
Effect of assumed shares under treasury stock method for stock options and restricted shares and if-converted method for convertible instruments	0.0	(3.3)
Income from the dilutive impact of subsidiary securities	0.0	0.0
Net (loss) income attributable to common stock, diluted	$ (29.7)	$ 135.7
Denominator for basic and dilutive earnings per share
Weighted-average Common stock outstanding (in shares)	44.8	44.3
Effect of assumed shares under treasury stock method for stock options and restricted shares and if-converted method for convertible instruments (in shares)	0.0	2.5
Weighted average common shares outstanding - diluted (in shares)	44.8	46.8
Net (loss) income attributable to participating security holders - basic (in dollars per share)	$ (0.66)	$ 3.14
Net (loss) income attributable to participating security holders - diluted (in dollars per share)	$ (0.66)	$ 2.90