Reconciliation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net Income (Loss)	$ 45.2	$ 41.4	$ 36.1
Weighted Average Common Shares Outstanding - Basic	16,045	15,991	15,373
Plus: Diluted Effect of Incremental Shares	8	5	3
Weighted Average Common Shares Outstanding - Diluted	16,053	15,996	15,376
Earnings per Common Share - Basic	$ 2.82	$ 2.59	$ 2.35
Earnings per Common Share - Diluted	$ 2.82	$ 2.59	$ 2.35