Shareholders' Equity - Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Weighted Average Number of Shares Outstanding [Line Items]
Weighted average number of common shares outstanding	56.7	58.9	61.0
Director Plan and deferred stock units	0.2	0.2	0.2
ESOP	0.2	0.2	0.1
Common shares outstanding—basic	57.1	59.3	61.3
Common and potential common shares outstanding—diluted	57.7	60.1	62.7
Restricted Stock
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect of stock awards	0.3	0.4	0.7
Stock Options
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect of stock awards	0.3	0.4	0.7