Summary of Restricted Stock and Restricted Stock Unit Award Activity (Detail) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock unit awards that vested during the period	330
Fair value of restricted shares that vested during the period	$ 5.6	$ 1.2
Compensation expense recognized during the period	4.2	4.2
Income tax benefit (cost) related to restricted stock awards	$ 0.8	$ (0.1)
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock unit awards that vested during the period	100	10
Fair value of restricted shares that vested during the period	$ 1.7	$ 0.3
Accumulated dividends paid upon vesting of restricted stock unit awards	0.3	0.1
Compensation expense recognized during the period	0.9	0.5
Income tax benefit (cost) related to restricted stock awards	$ 0.3	$ (0.1)

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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