Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Earnings
Net income	$ 4.3	$ 1.3
Shares
Weighted-average common shares outstanding (basic shares)	45.3	45.9
Adjustment for assumed dilution:
Weighted-average shares assuming dilution (diluted shares)	45.4	46.0
Earnings per share
Basic and diluted (in dollars per share)	$ 0.09	$ 0.03
Restricted stock units
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.0	0.1
Performance shares
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.0

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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