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Retirement Benefit Obligations - Additional Information (Detail)
$ in Millions
3 Months Ended
Mar. 31, 2021
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Company's contributions $ 0.7
Other Postretirement Benefit Plans, Defined Benefit  
Defined Benefit Plan Disclosure [Line Items]  
Company's contributions 0.4
Supplemental Employee Retirement Plans, Defined Benefit  
Defined Benefit Plan Disclosure [Line Items]  
Benefit payments under SERP Plan 0.2
Expected additional benefit payments for the remainder of 2020 $ 0.4