Earnings Per Share - Computation of Basic and Diluted Net Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2025	Jun. 30, 2024
Numerator:
Net income	$ 89.5	$ 139.4	$ 68.0	$ 247.2	$ 228.9	$ 315.2
Denominator:
Basic weighted average shares outstanding	56,117		56,451		56,045	56,499
Diluted weighted average shares outstanding	56,500		56,771		56,324	56,548
Earnings per share:
Earnings per share, basic	$ 1.59		$ 1.2		$ 4.08	$ 5.58
Earnings per share, diluted	$ 1.58		$ 1.2		$ 4.06	$ 5.57
Restricted Stock Units [Member]
Denominator:
Dilutive effect of unvested restricted stock and restricted stock units	383		320		279	49