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Stock-Based Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2021 | Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock option compensation | $ 2.9 | $ 2.8
Stock Options Plan [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number exercisable and fully vested | 87,136 |
Fully vested stock options with performance conditions attached | 65,176 |
Stock option compensation | $ 2.9 | 2.8
Total intrinsic value exercised | 1.7 | 4.6
Total compensation cost related to non-vested stock options not yet recognized | $ 10.5 |
Expected compensation cost recognized over the weighted-average period | 2 years 1 month 24 days |
Stock Equivalent Units [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Fully vested stock options with performance conditions attached | 27,935 |
Total intrinsic value exercised | $ 1.3 | 6.1
Expected compensation cost recognized over the weighted-average period | 2 years 29 days |
Number of exercisable SEUs | 32,132 |
Compensation cost | $ 2.9 | $ 3.0

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