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Goodwill and Other Intangible Assets - Schedule of Estimated Annual Amortization Expense Related to Other Intangible Assets (Detail) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]    
2021 (excluding the nine months ended September 30, 2021) $ 0.3  
2022 1.0  
2023 0.9  
2024 0.7  
2025 0.7  
2026 and thereafter 5.5  
Net Book Value $ 9.1 $ 9.8