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Stock-Based Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions | 9 Months Ended
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Sep. 30, 2021 | Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock option compensation | $ 4.6 | $ 4.4
Stock Options Plan [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number exercisable and fully vested | 86,836 |
Fully vested stock options with performance conditions attached | 66,776 |
Stock option compensation | $ 4.6 | 4.4
Total intrinsic value exercised | 1.8 | 4.7
Total compensation cost related to non-vested stock options not yet recognized | $ 8.8 |
Expected compensation cost recognized over the weighted-average period | 2 years 7 days |
Stock Equivalent Units [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Fully vested stock options with performance conditions attached | 22,574 |
Total intrinsic value exercised | $ 1.6 | 6.3
Expected compensation cost recognized over the weighted-average period | 1 year 10 months 20 days |
Number of exercisable SEUs | 26,771 |
Compensation cost | $ 3.4 | $ 4.9

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