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Stock-Based Compensation Plans (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	May 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved for issuance (in shares)			5,485,000
Shares available for future grants (in shares)	394,000
Number of stock options granted	0	0
Stock-based compensation expense	$ 7.9	$ 2.9
Aggregate intrinsic value of options exercised	4.5	6.6
Cash received from option exercises	$ 3.4	$ 9.0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term	7 years
Stock options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Stock options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
Restricted shares \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Restricted shares \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
LTIP awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Term	7 years
LTIP awards \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance based award payouts	0.00%
LTIP awards \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance based award payouts	150.00%
Performance-based stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Performance period	3 years