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Reclassifications out of Accumulated Other Comprehensive Loss - Summary of Reclassifications out of Accumulated Other Comprehensive Loss (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2020
USD ($)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]  
Total reclassifications $ (1.1)
Defined Benefit Pension Plan Items [Member]  
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]  
Total reclassifications (1.1)
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member]  
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]  
Total before tax 1.2
Income tax expense (0.1)
Total reclassifications 1.1
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member] | Defined Benefit Pension Plan Items [Member]  
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]  
Amortization of prior service credit (0.5)
Amortization of actuarial net losses $ 1.7