Earnings per Share - Reconciliation of Numerator and Denominator of Basic and Diluted Earnings per Share Calculation and Anti-dilutive Share-based Awards (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share Basic And Diluted [Line Items]
Basic	$ 0.21	$ 0.43	$ 0.29	$ 0.90
Diluted	$ 0.21	$ 0.43	$ 0.29	$ 0.89
Net earnings	$ 7.1	$ 14.7	$ 9.9	$ 30.6
Weighted average number of common shares outstanding	34.0	34.2	34.0	34.1
Dilutive awards	0.2	0.1	0.0	0.1
Diluted weighted average number of common shares outstanding	34.2	34.3	34.0	34.2
Total weighted average number of anti-dilutive share-based awards	1.1	1.1	1.9	1.5
Restricted stock units
Earnings Per Share Basic And Diluted [Line Items]
Total weighted average number of anti-dilutive share-based awards	0.4	0.3	1.1	0.7
Stock options
Earnings Per Share Basic And Diluted [Line Items]
Total weighted average number of anti-dilutive share-based awards	0.7	0.8	0.8	0.8