Equity Earnings Per Share - Computation of Basic and Diluted Earnings (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income, basic and diluted	$ 35.5	$ 39.9	$ 2.0	$ (3.7)	$ 35.1	$ 9.4	$ 9.7	$ (6.7)	$ 73.7	$ 47.5	$ 69.1
Denominator:
Basic weighted average common shares (in shares)									29.1	28.7	28.4
Stock options, RSUs and PSUs (in shares)									0.3	0.4	0.5
Weighted average shares used to calculate diluted earnings per share (in shares)									29.4	29.1	28.9
Earnings per share:
Basic (in USD per share)	$ 1.22	$ 1.37	$ 0.07	$ (0.13)	$ 1.22	$ 0.33	$ 0.34	$ (0.23)	$ 2.53	$ 1.66	$ 2.43
Diluted (in USD per share)	$ 1.19	$ 1.35	$ 0.07	$ (0.13)	$ 1.20	$ 0.32	$ 0.33	$ (0.23)	$ 2.51	$ 1.63	$ 2.39
Antidilutive stock options, RSUs and PSUs
Earnings per share:
Antidilutive stock options, RSUs and PSUs (in shares)									0.4	0.3	0.2