Shareholders' Equity - Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Weighted Average Number of Shares Outstanding [Line Items]
Weighted average number of common shares outstanding	56.0	56.7	58.9
Director Plan and deferred stock units	0.3	0.2	0.2
ESOP	0.2	0.2	0.2
Common shares outstanding—basic	56.5	57.1	59.3
Common and potential common shares outstanding—diluted	56.8	57.7	60.1
Restricted Stock
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect of stock awards	0.3	0.3	0.4
Stock Options
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect of stock awards	0.0	0.3	0.4