Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020	Jun. 30, 2019
Basic:
Net earnings	$ 39.1		$ 32.6		$ 89.2	$ 58.6
Weighted average shares of common stock outstanding (in shares)	149.2	[1]	147.7	[1]	148.6	147.6
Basic net earnings per share (in dollars per share)	$ 0.26		$ 0.22		$ 0.60	$ 0.40
Shares used for diluted net earnings per share:
Weighted average shares of common stock outstanding (in shares)	149.2	[1]	147.7	[1]	148.6	147.6
Weighted average shares of common stock, diluted (in shares)	150.0	[1]	148.5	[1]	149.3	148.4
Diluted net earnings per share (in dollars per share)	$ 0.26		$ 0.22		$ 0.60	$ 0.39
Common Class A
Basic:
Weighted average shares of common stock outstanding (in shares)	149.2		147.7		148.6	147.6
Shares used for diluted net earnings per share:
Weighted average shares of common stock outstanding (in shares)	149.2		147.7		148.6	147.6
Dilutive effect of unvested restricted shares of Class A common stock (in share)	0.8		0.8		0.7	0.8

[1] Net of income tax benefit of $0.5 million and $0.6 million for the three and six months ended June 30, 2020, respectively, and $0.8 million and $0.9 million for the three and six months ended June 30, 2019, respectively.