Shareholders' Equity - Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average number of common shares outstanding (in shares)	56.5	57.0
Director Plan and deferred stock units (in shares)	0.2	0.2
ESOP (in shares)	0.2	0.2
Common shares outstanding - basic (in shares)	56.9	57.4
Common and potential common shares outstanding - diluted (in shares)	57.2	58.1
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive effect of stock (in shares)	0.2	0.4
Stock options award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive effect of stock (in shares)	0.1	0.3