Earnings Per Share - Calculations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disclosure Earnings Per Share Calculations Of Basic And Diluted Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share		$ 5.28	$ 4.75	$ 5.07
Calculation of Basic Earnings Per Share:
Net Income		$ 118.6	$ 87.2	$ 89.8
Weighted shares outstanding - Basic (in shares)	[1]	22,469	18,371	17,722
Basic Earnings Per Share (in usd per share)		$ 5.28	$ 4.75	$ 5.07
Calculation of Diluted Earnings Per Share:
Net Income		$ 118.6	$ 87.2	$ 89.8
Reconciliation of Denominator:
Weighted shares outstanding - Basic (in shares)	[1]	22,469	18,371	17,722
Share-based Compensation		62	64	82
Adjusted denominator — Diluted	[1]	22,531	18,435	17,804
Income (Loss) from Continuing Operations, Per Diluted Share		$ 5.26	$ 4.73	$ 5.04
Diluted (in usd per share)		$ 5.26	$ 4.73	$ 5.04

[1] ) 2023 and 2024 weighted average shares reflect the impact of 4.4 million common shares issued in November 2023 in connection with the acquisition of FCG. See Notes 4 and 15 for additional details on the acquisition and related equity offering.